Xi Jinping, who is expected to be unveiled as China’s next president in October, has not been seen in public for ten days leading to a flurry of online speculation about his health. 
 
 The Communist party has so far refused to explain Mr Xi’s disappearance and a foreign ministry spokesperson again declined to comment on Tuesday. 
 
 “I hope you can ask more serious questions,” Hong Lei told reporters in Beijing after being asked if Mr Xi was even still alive. 
 
 Initial rumours suggested Mr Xi had hurt his back swimming or playing football. However, the New York Times cited a well-connected political analyst yesterday who claimed Mr Xi might have suffered a “mild heart attack”. 
 
 One source told Reuters he had injured his back during his “daily swim”. But another anonymous source appeared to contradict that version, saying: “He’s unwell, but it’s not a big problem.” 
 
 One senior journalist from a Beijing admitted he was flummoxed by Mr Xi’s sudden and unexpected disappearance. 
 
 “We are all waiting for an announcement,” the journalist said, adding that he had heard rumours that a “major news [bulletin]” on state-controlled TV was imminent. 
 
 Chinese internet censors attempted to stem the flow of online rumours that had the country’s hugely popular social media networks buzzing. A series of related search terms on social media, including “back injury” and “vice president”, were blocked, along with Mr Xi’s name. 
 
 But micro-bloggers soon found their way around the censors, using terms such as “crown prince” to escape detection. 
 
 “The rumours about the crown prince are flying everywhere,” wrote one in reference to Mr Xi, whose name had already been blocked. “The Congress is approaching. Come out, crown prince, to calm people down.” 
 
 Questions over the whereabouts of Mr Xi, 59, began last Wednesday after authorities cancelled the vice-president’s meeting with Hillary Clinton, the US secretary of state, citing “unexpected scheduling reasons”. 
 
 Last Friday, Mr Xi was not listed as having attended a high-level meeting of the central military commission, of which he is the vice-chairman. 
 
 On Monday, with Mr Xi still nowhere to be seen, those whispers grew into widespread speculation. A meeting with Helle Thorning-Schmidt, the Danish prime minister, which had been announced to media last Wednesday, also appeared to have been axed. 
 
 The Chinese foreign ministry later denied, however, that the meeting had ever been planned. 
 
 Despite the rumours, some of China’s top officials continued to travel outside Beijing, which would seem unlikely if the leadership was consumed with crisis. 
 
 Premier Wen Jiabao gave a speech in the northern port city of Tianjin, and his likely successor, Vice Premier Li Keqiang, was visiting a northwestern region, according to state media reports. 
 
 Analysts have dismissed the most sensational online claims, posted on a US website and subsequently retracted, that Mr Xi had suffered an assassination attempt as part of an internal struggle for power struggle. 
 
 “If that did happen or if the party leadership believed that such an attempt was made I think you would have Beijing crawling with police and security forces,” said Steve Tsang, a China expert from the University of Nottingham. 
 
 “Nobody has seen [that happen] and we are talking about a government that habitually over reacts. So I really don’t buy that.” 
 
 Prof Tsang said the most likely explanation was a medical condition “that makes it impossible to parade him on TV”. 
 
 Hu Xingdou, a professor from the Beijing Institute of Technology who blogs on political and social issues, said Mr Xi’s absence was “quite normal”. 
 
 “He might have some health problems. He might have fallen ill due to overwork. Anyone can get sick. It is normal for a student to take a week off school if they fall in,” he said. 
 
 But Prof Hu criticised a lack of government transparency in handling the case. “Rumours die when you open up,” he said. 
 
 Mr Xi’s withdrawal from public view comes at a crucial time for Chinese politics, with the once-in-a-decade power transition widely expected to take place before the end of October with the opening of the 18th Communist Party Congress. It also follows the messy fallout from the Neil Heywood murder scandal, which toppled Bo Xilai, once one of China’s most powerful men. 
 
 But Prof Tsang said there was “no evidence that Xi Jinping’s succession was in trouble [or] that there are powerful people or groups in the top leadership who are now trying to derail his succession.” ||||| BEIJING—Speculation gathered steam about the health and whereabouts of the man expected to take the reins as China's top leader in a matter of weeks as Chinese authorities keep their usual tight grip on information about the nation's leaders. 
 
 Xi Jinping hasn't been seen since Sept. 1, raising questions about the whereabouts and health of the presumed next president of China. Jeremy Page has more. Photo: AP 
 
 Monday, Chinese authorities failed to explain why Vice President Xi Jinping, who hasn't been seen in public since Sept. 1, had missed another meeting with a visiting foreign dignitary, Denmark's prime minister. 
 
 Rumors that all wasn't well with 59-year-old Mr. Xi were sparked last week when he skipped a meeting with visiting U.S. Secretary of State Hillary Clinton at the last minute. The government declined to provide a clear explanation for that highly unusual move. 
 
 The mystery adds to an already tense atmosphere ahead of once-a-decade leadership transition expected to kick into gear in a few weeks. President Hu Jintao is due to hand over to Mr. Xi his most powerful post, as Communist Party chief. 
 
 Despite government efforts to crack down on online commentary, Mr. Xi was the subject of speculation on fast-moving microblogs, which work like Twitter. 
 
 "Jinping, what's the deal?" read one post on Sina Corp.'s popular Weibo microblogging service, which used Mr. Xi's given name and had been left untouched by censors Monday evening. "The entire country from top to bottom is paying attention." 
 
 View Slideshow Narong Sangnak/European Pressphoto Agency During his December trip to Thailand, Mr. Xi met with Thai Prime Minister Yingluck Shinawatra, right, in Bangkok. 
 
 As is often the case with China's top leaders, Chinese and English language searches for Mr. Xi's full name and surname were blocked on Weibo on Monday. But searches for "Jinping" weren't blocked in Chinese, though periodic searches using those characters produced fewer results each time, suggesting censors were busy deleting posts about Mr. Xi. 
 
 Even as Chinese society has opened to the outside world, a shroud of secrecy continues to surround virtually every aspect of Chinese leaders' personal lives, and their health is hardly ever discussed by authorities. Leaders rarely open themselves to direct questions; for example, Premier Wen Jiabao usually takes questions from media only at one tightly scripted news conference a year. 
 
 Chinese leaders sometimes don't appear in public for extended periods, with no explanation, but it is very unusual for one to cancel meetings with foreign officials at such short notice, according to party insiders, diplomats and political analysts. 
 
 A U.S. official said last week that Mr. Xi canceled his meeting with Mrs. Clinton on Wednesday because of a back problem. Since then, Chinese social-media sites have been buzzing with speculation that Mr. Xi strained his back either swimming or playing soccer. China's government hasn't commented on his health. 
 
 Mr. Xi's visit to the U.S. last February carried all the trappings of an extended introduction of the coming Chinese leader. He was presented in appearances across the country as warm, good-humored politician, in marked contrast to the country's tradition of stern, sober rulers. 
 
 That display makes his absence now all the more mysterious as well as interesting—although U.S. officials guard carefully against any public remark that might offend the Chinese. After all, there could be many explanations for Mr. Xi's absence. 
 
 "The bottom line is that there is no reliable information to go on," said Kenneth Lieberthal, a White House official during the Bill Clinton administration and now with the Brookings Institution, a think tank. "Something is amiss—otherwise, they would have found an opportunity for him to be seen. But whether he hurt his back or there is some other problem is something that at this point there is no way to know with confidence." 
 
 Plans for a smooth leadership transition have already been thrown into disarray by the scandal surrounding Bo Xilai, the ousted party leader who was once a candidate for the top leadership but whose wife, Gu Kailai, was convicted last month of murdering a British businessman. 
 
 Rumors about leaders have sometimes prompted the party into quick action, such as last year when Hong Kong media reported that Jiang Zemin, the former president, had died after being rushed to a military hospital with heart problems. The state-run Xinhua news agency—the main government media organ—dismissed the reports about Mr. Jiang at the time as "pure rumor." Mr. Jiang later appeared on state media. 
 
 Enlarge Image Close Agence France-Presse/Getty Images Hillary Clinton at the APEC summit in Vladivostok, Russia, Saturday. 
 
 When Chinese social-media sites began circulating reports this year that Zhou Yongkang, the domestic security chief, was in political trouble for supporting Mr. Bo, state media ran a series of lengthy reports showing Mr. Zhou attending public events. 
 
 So far, however, state media have made little attempt to suppress the rumors surrounding Mr. Xi, although one party newspaper, Study Times, did put on its front page Monday a transcript of the speech he made at his Sept. 1 appearance. China's Foreign Ministry said last week that the cancellation of Mr. Xi's meeting with Mrs. Clinton was a normal "adjustment of itinerary," and Foreign Minister Yang Jiechi said there shouldn't be "unnecessary speculation" about the move. But neither gave a reason for the cancellation. 
 
 A senior U.S. State Department official said Mr. Xi had also canceled an appearance with Singapore Prime Minister Lee Hsien Loong. 
 
 Mr. Xi has probably an additional couple of days to appear publicly before public pressure forces the Chinese government to at least issue a statement explaining Mr. Xi's status, said Christopher Johnson, a former top China analyst at the Central Intelligence Agency who is now a senior adviser on China at the Center for Strategic and International Studies. 
 
 "My sense of it is if he were physically able to show up and be seen publicly, he'd do it, unless it's political," Mr. Johnson said, adding that the Chinese government's reversal of its message that Mr. Xi would be available for a meeting and photo opportunity on Monday suggests Mr. Xi is having health problems. 
 
 "As the incoming leader for the next decade, Xi should be the picture of health," Mr. Johnson said. "If he's not, that's definitely a situation for the party leadership." 
 
 Enlarge Image Close Associated Press Xi at his last appearance Sept. 1. 
 
 Mr. Xi had been scheduled to meet Danish Prime Minister Helle Thorning-Schmidt during her visit to China, according to a person close to the planning. However, Chinese and Danish officials both said Monday that Ms. Thorning-Schmidt wouldn't be meeting Mr. Xi during her three-day trip. 
 
 She was received by Vice Premier Wang Qishan at a welcoming ceremony in the Zhongnanhai leadership compound in Beijing on Monday and was due to meet Premier Wen Jiabao in the nearby city of Tianjin on Tuesday, according to the Danish Embassy. 
 
 The person close to the planning of her trip said Mr. Xi's cancellation wasn't a reflection of Denmark's relationship with China. "He also canceled Clinton," the person said. "It's not about Denmark." 
 
 Hong Lei, a Chinese Foreign Ministry spokesman, declined to say whether a meeting with Mr. Xi had been scheduled and then canceled, telling a regular news briefing Monday: "As agreed between the Chinese and Danish sides, leaders of China's State Council will meet the Danish prime minister." 
 
 Asked about Hong Kong media reports that Mr. Xi had been injured in a car crash, he declined further comment. 
 
 While the speculation surrounding Mr. Xi is primarily focused on his health, part of what unnerves the Chinese public is that similar radio silence has at times in China's past been due to a power struggle behind the scenes. 
 
 Rumors about Mr. Bo intensified after he failed to appear alongside other Politburo members at a session of the national parliament meeting on March 8. He told a news conference the next day that he had been ill, but he was dismissed as party chief of Chongqing within a week. 
 
 —Siobhan Gorman and Keith Johnson in Washington contributed to this article. 
 
 Write to Jeremy Page at jeremy.page@wsj.com, Flemming Emil Hansen at Flemming.Hansen@dowjones.com and Josh Chin at josh.chin@wsj.com 
 
 A version of this article appeared September 11, 2012, on page A1 in the U.S. edition of The Wall Street Journal, with the headline: China Mystery: Where Is Xi Jinping?. ||||| BEIJING China's top leader-in-waiting Xi Jinping, who has set off a storm of rumors after not showing up at scheduled public events for more than a week, is nursing an ailment, possibly a back injury suffered while swimming, sources said on Tuesday. 
 
 Xi, who is due to take over the presidency of the world's second-largest economy in March next year, has skipped several meetings with visiting foreign leaders and dignitaries over the past week, including U.S. Secretary of State Hillary Clinton and the prime ministers of Singapore and Denmark. 
 
 China's government, however, has declined to spell out what is ailing Xi, 59 - in keeping with decades of official secrecy over the health of senior leaders, a tradition viewed in the West as out of step with a modern state and emerging superpower. 
 
 "Xi injured his back when he went for his daily swim," a source close to the Beijing leadership said after Xi's absence from the public stage was first noticed last week. At that stage, he had failed to keep scheduled meetings with Clinton and Singapore Prime Minister Lee Hsien Loong. 
 
 The source declined to give further details on the injury, including exactly when and where the incident took place. 
 
 Another source also said the injury happened when Xi went swimming. "Xi pulled a (back) muscle when he went swimming," the source said. 
 
 A third source, citing people close to Xi, said: "He's unwell, but it's not a big problem." 
 
 All three sources spoke on condition of anonymity. 
 
 The lack of an official explanation has fuelled Internet speculation surrounding Xi's condition, and brought some pointed questions at briefings by China's foreign ministry. 
 
 On Tuesday, the ministry's spokesman Hong Lei was asked whether Xi is in good health. Sticking to his government's usual reticence, Hong said he had no information to give. But he appeared dismissive of any hint that Xi might be in a bad way. 
 
 "I hope you can ask a serious question," Hong said when asked to confirm that Xi was alive. 
 
 SEARCHES BLOCKED 
 
 China's popular Twitter-like microblogging site Sina Weibo blocked searches for Xi's name, as is common with top leaders, but users as usual found ways to skirt the restrictions, referring to Xi as "the crown prince". 
 
 "What's up with the crown prince? He's vanished for the last 10 days or so and the whole world is wondering where he is," wrote one user. 
 
 Despite the panicky rumors, some of China's top officials continued to travel outside Beijing -- not what would be expected if the leadership was consumed with crisis. Premier Wen Jiabao gave a speech in the northern port city of Tianjin, and his likely successor, Vice Premier Li Keqiang, was visiting a northwestern region, according to state media reports. 
 
 Xi had been scheduled to meet visiting Danish Prime Minister Helle Thorning-Schmidt on Monday afternoon for a photo opportunity, according to a media advisory that had been circulated on September 5. But the event did not take place. 
 
 Thorning-Schmidt told Reuters in an interview that a meeting with Xi had never been on her program, which was released on Friday. 
 
 "I think there has been a slight misunderstanding," she said. "I would, of course, very much like to see him (Xi) and I think I will see him at some stage, perhaps on my next visit to China, but he was never in my program which we released on Friday, so there shouldn't be anything new in my not seeing him." 
 
 The foreign ministry's website shows Xi's most recent public appearance was at a ceremony at the ruling Communist Party's Central Party School in Beijing on September 1. 
 
 The rumors about Xi come at a tempestuous time for Chinese politics. The 18th Communist Party Congress, at which China's next top leaders including Xi are likely to be unveiled, is set to take place in October. 
 
 Earlier this year, senior politician Bo Xilai, once seen as a candidate for the top rung of party leadership, was suspended from the Politburo and his wife convicted of murdering a British businessman. The wife, Gu Kailai, was given a suspended death sentence last month. 
 
 In another scandal this month, a senior ally of President Hu Jintao was demoted after sources said the ally's son was involved in a deadly crash involving a luxury sports car. 
 
 China has been engulfed in the past by rumors about senior leaders. 
 
 Last year, the official Xinhua news agency was forced to come out with a one-line statement in English denying former President Jiang Zemin had died, following feverish online speculation and a report from a Hong Kong television station. 
 
 (Reporting by Ben Blanchard, Sui-Lee Wee, Chris Buckley, Don Durfee, Michael Martina and Nick Edwards; Editing by Alex Richardson and Jeremy Laurence) ||||| Mr. Xi was designated internally as the presumptive heir to Mr. Hu as the leader of the Communist Party, head of state and chairman of the top military oversight body in 2007, a full five years before he was expected to assume those posts. Party bosses have tried to name future leaders well in advance to prevent destabilizing jockeying for power. Smooth transitions are considered by many Chinese as a crucial test of the Communist Party’s longevity, and its leaders are eager to make the case that their authoritarian system can manage China better than a multiparty democracy could. 
 
 Analysts who follow Chinese politics say the transition is still likely to happen roughly along the planned lines. They also say that the core leadership team around Mr. Xi is slowly taking shape, with the lineup of the Standing Committee coming into focus as the congress draws near. 
 
 But at the very least, the atmospherics are turning out to be far messier than envisioned, with officials stumbling to maintain their usual careful choreography. 
 
 Last Wednesday, after Mr. Xi did not meet Mrs. Clinton and Prime Minister Lee Hsien Loong of Singapore , diplomats said privately that he had a bad back. 
 
 On Monday, the situation got odder. Foreign journalists had been invited to a photo opportunity between Mr. Xi and Prime Minister Helle Thorning-Schmidt of Denmark. On Monday, however, the Foreign Ministry denied that any such meeting had been scheduled and said other Chinese officials would meet the Danish leader. 
 
 “We have told everybody everything,” said a Foreign Ministry spokesman, Hong Lei. 
 
 While Chinese leaders often do not appear in public for long periods, canceling meetings with foreign dignitaries at the last minute is highly unusual. Adding to the uncertainty is the lack of an official statement of any kind, with observers speculating about car crashes and heart attacks. 
 
 “There’s every sort of crazy rumor about Xi’s health,” said a senior Chinese journalist, who asked not to be identified because of the sensitivity surrounding the case. “But no one is saying anything.” 
 
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 Mr. Xi’s absence comes during a year when the Chinese political system has suffered serious blows. 
 
 This spring, the senior leader Bo Xilai vanished from view, and soon after, his wife was charged with murdering a British businessman. She was eventually tried and convicted over the summer, and his police chief, Wang Lijun, who has been accused of covering up the murder and other crimes, could face trial soon. 
 
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 The scandal threatened to upset the complex political calculations that underlie the transition because Mr. Bo was popular among an influential wing of reform skeptics, many of whom condemn the country’s widening wealth gap. So even though Mr. Bo’s own case still has not been handled, sorting out his wife and closest associates was seen as an important step to get the transition back on track, implying that senior leaders were united on how to deal with Mr. Bo. 
 
 But no sooner had these problems been cleared than one of Mr. Hu’s closest allies was sidelined in unusual circumstances. 
 
 The ally, Ling Jihua, had headed the party’s General Office, a position similar to chief of staff. He was expected to be replaced so that Mr. Xi could bring in his own man, but he departed the position unusually early for a job that many saw as a demotion. 
 
 Some sources say it was because of a car crash earlier this year involving a Ferrari: his son was at the wheel and died, and two female companions were seriously injured. The episode exposed the fabulous wealth and extravagant lifestyles that some leaders’ family members acquire. 
 
 Adding to the uncertainty is that no date has been set for the party congress. Political experts expected the date to be set by now, contributing to speculation that the final lineup of the new leadership remains unsettled. 
 
 Party congresses are held every five years, generally in October. In 2007, the year of the previous congress, the October date had been announced by August. 
 
 “These are not signs that everything is going well,” said Bo Zhiyue, a political science professor at the National University of Singapore. “Negotiations seem to be going on.” 
 
 China’s political system has long been a black box, but its all-encompassing secrecy has begun to seem anachronistic as the country has become one of the world’s biggest economic, political and military powers. 
 
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 “Authorities are worried about anything that may tarnish the transition,” said Joseph Y. S. Cheng, a political science professor at the City University of Hong Kong . “But this concern is working against their interests; they should come out with a clear statement” about Mr. Xi’s whereabouts. 
 
 Mr. Xi could appear publicly at any time and quash the speculation about his status. But for now rumors are replacing real information, with one of the most common being that he hurt his back playing sports. Popular Internet search sites have aggressively removed references to Mr. Xi and have even blocked searches for “back injury.” 
 
 One well-connected political analyst in Beijing said that Mr. Xi had suffered a mild heart attack but that it was not serious enough to prevent him from assuming China’s top positions. 
 
 “They say it won’t affect the party meeting,” the analyst said. 
 
 As if to assuage worries about Mr. Xi’s health, a newspaper on Monday ran a picture of Mr. Xi addressing students at the opening of the fall semester of the Central Party School. The photo and speech, however, were from Sept. 1, the last confirmed date of Mr. Xi’s being seen in public.
– The global rumor mill is swirling around the sudden conspicuous absence of Xi Jinping, who is scheduled to ascend to China's presidency in a matter of weeks. Xi hasn't been seen in public in 10 days, according to the Telegraph, and last week he took the unheard of step of canceling three meetings with top foreign officials, including Hillary Clinton. Yesterday, officials turned journalists away from a planned photo-op between Xi and Denmark's prime minister, denying it had ever been scheduled. Officials tell Reuters Xi hurt his back while swimming, but speculation of worse is rampant. One source tells the New York Times that Xi may have suffered a mild heart attack, and an earlier report, since retracted, alleged that a military official tried to assassinate him, and wound up injuring him in a car accident. Amid the speculation, China has blocked all Internet searches for his name, the Wall Street Journal reports. "Something is amiss," a Brookings Institute member says. "Otherwise, they would have found an opportunity for him to be seen.