SEOUL North Koreans poured into the streets on Monday to mourn the death of leader Kim Jong-il and state media hailed his untested son as the "Great Successor" of the reclusive state whose atomic weapons ambitions are a major threat to the region. 
 
 Earlier, a tearful North Korean television announcer, dressed in black and her voice quavering, said the 69-year old ruler died on Saturday of "physical and mental over-work" on a train on his way to give "field guidance" -- advice dispensed by the "Dear Leader" on trips to factories, farms and the military. 
 
 Security concerns over North Korea, which in 2010 shelled civilians on a South Korean island and is accused of sinking one of its warships earlier that year, were heightened after Seoul said the North had test-fired a short range missile shortly before the announcement of Kim's death. 
 
 It was the first known launch since June and South Korea's defense ministry said it might abandon plans to light Christmas trees on the border, something the North has warned could provoke retaliation. 
 
 Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff, said the missile test had likely been planned before Kim's death and U.S. officials said the military had so far not raised alert levels for some 28,500 U.S. troops in South Korea. 
 
 'UTTER DESPAIR' 
 
 North Korea's official KCNA news agency lauded Kim's youngest son, Kim Jong-un as "the outstanding leader of our party, army and people." 
 
 A KCNA dispatch said North Koreans from all walks of life were in utter despair but were finding comfort in the "absolute surety that the leadership of Comrade Kim Jong-un will lead and succeed the great task of revolutionary enterprise." 
 
 There was uncertainty about how much support the third generation of the North's ruling dynasty has among the ruling elite, especially in the military, and concern that he might need a military show of strength to help establish his credentials. 
 
 "Kim Jong-un is a pale reflection of his father and grandfather. He has not had the decades of grooming and securing of a power base that Jong-il enjoyed before assuming control from his father," said Bruce Klingner, an Asia policy analyst at the Heritage Foundation in Washington. 
 
 "(He) may feel it necessary in the future to precipitate a crisis to prove his mettle to other senior leaders or deflect attention from the regime's failings." 
 
 Chinese state television showed North Koreans crying in the capital of Pyongyang. KCNA reported people were "writhing in pain" after losing the man who in 1994 succeeded his father Kim Il-sung, the North's first -- and officially eternal -- president as leader of the totalitarian state. 
 
 An "endless stream" of soldiers, working people and students visited a massive memorial of Kim Il-sung in central Pyongyang mourning the death of the "Dear Leader" until past midnight. "They are weeping bitterly out of self-reproach and regret that they failed to keep Kim Jong-il in good health," KCNA said. 
 
 Kim will be laid to rest next to his father, the agency said. The funeral of Kim Jong-il, turned into a demi-god by his propaganda machine, will be held on December 28. 
 
 News of the death of the man whose push to build a nuclear arsenal left the North heavily sanctioned and internationally isolated, triggered immediate nervousness in the region, with South Korea stepping up its military alert. 
 
 China, North Korea's neighbor and only powerful ally, said it was confident the North would remain united and that the two countries would maintain their relationship. 
 
 Expressing grief at Kim's death, China's Foreign Ministry spokesman Ma Zhaoxu was quoted by Xinhua news agency as saying, "We are confident the North Korean people will be able to turn their anguish into strength and unify as one." 
 
 There was less regret from Western leaders, with Canadian Prime Minister Stephen Harper saying Kim had "violated the basic rights of the North Korean people for nearly two decades." 
 
 Western officials sought to put a positive spin on Kim's passing, suggesting the new leadership had a chance to engage with the world. U.S. Secretary of State Hillary Clinton voiced "hope for improved relations with the people of North Korea." 
 
 Clinton also said she had been in touch with other participants in stalled six-nation talks on North Korea's nuclear program but did not elaborate. Washington and its main Asian allies have resisted calls to resume the talks, saying Pyongyang must first halt provocative actions. 
 
 While his father had 20 years as official heir, Kim Jong-un only became successor by taking on official titles last year, months after Kim Jong-il suffered a stroke around August 2008. 
 
 He takes over an economy that has been ravaged by years of mismanagement under Kim Jong-il, who only briefly flirted with economic reform, preferring to stick with central planning and the brutal crushing of any opposition. 
 
 Under Kim Jong-il's rule, an estimated one million North Koreans died during a famine in the 1990s. Even with good harvests, the state cannot feed its 25 million people. 
 
 Little is known of Kim Jong-un, who is believed to be in his late 20s and to have studied briefly at a school in Switzerland. 
 
 KCNA said Kim Jong-il died on Saturday after "an advanced acute myocardial infarction, complicated with a serious heart shock." 
 
 South Korea, still technically at war with the North, placed its troops and all government workers on emergency alert, but said there were no signs of any unusual North Korean troop movements. 
 
 The United States said it was committed to its allies and to stability on the divided Korean peninsula. Across the heavily armed border with South Korea, the North maintains an estimated one million troops, one of the world's largest standing armies. 
 
 Japan said it was watching developments closely. "We hope this sudden event does not have an adverse effect on the peace and stability of the Korean peninsula," Chief Cabinet Secretary Osamu Fujimura said after a hastily called ministerial meeting on security. 
 
 SHARES FALL 
 
 Fears of what might happen next in North Korea unsettled financial markets, with Asian shares and U.S. index futures falling. South Korean stocks tumbled up to 5 percent, and the U.S. dollar strengthened. The Korean won fell 1.8 percent. 
 
 Kim Jong-un was at the head of a long list of officials making up the funeral committee, indicating that he would lead it and had taken, or been given, charge. 
 
 Zhu Feng, Professor of International Relations at Peking University, said it was clear the mechanism for transition was in place and working. 
 
 "In the short term, there won't be new policies, only a stressing of policy stability and continuity. So soon after Kim Jong-il has died, no leader will dare say that an alternative policy course is needed," Zhu said. 
 
 Chung Young-Tae at the Korea Institute of National Unification said there was "a big possibility that a power struggle may happen." 
 
 UNCHALLENGED HEAD 
 
 Kim Jong-il also promoted his sister and her husband, Jang Song-thaek, to important political and military posts, creating a powerful triumvirate. 
 
 Jang is seen as effective regent for the younger Kim. He holds a top position in the ruling Worker's Party, providing some balance to the generals who have been seen as more hardline in pushing the North to develop an atomic arsenal. 
 
 Experts say Kim Jong-un has the intelligence and leadership skills to make him suited to succeed his father. He is reported to have a ruthless streak that analysts say he would need to rule North Korea. 
 
 Pyongyang, which tested a nuclear device in 2006 and again in May 2009, last year unveiled a uranium enrichment facility, giving it a second route to make an atomic bomb along with its plutonium program. 
 
 Mark Fitzpatrick of the International Institute for Strategic Studies in London said that while a crisis would probably not erupt immediately, Pyongyang would not agree to the steps Seoul and Washington are demanding to restart the six-party talks. 
 
 "If it wasn't ready to countenance such steps under the paramount leader, it surely won't do it immediately after his death," he said. 
 
 (Additional reporting by Seoul, Washington and Asian bureaux. Editing by Jonathan Thatcher, Patrick Worsnip, David Storey and Christopher Wilson) ||||| Media playback is unsupported on your device Media caption The BBC's Lucy Williamson says news of the death has taken people by surprise 
 
 North Korean leader Kim Jong-il has died of a heart attack at the age of 69, state media have announced. 
 
 Millions of North Koreans were "engulfed in indescribable sadness", the KCNA state news agency said, as people wept openly in Pyongyang. 
 
 KNCA described one of his sons, Kim Jong-un, as the "great successor" whom North Koreans should unite behind. 
 
 Pyongyang's neighbours are on alert amid fears of instability in the poor and isolated nuclear-armed nation. 
 
 This could be a turning point for North Korea William Hague, UK Foreign Minister World reactionDeath triggers swift reaction 
 
 Fears were compounded by unconfirmed reports from South Korean news agency Yonhap that the North had test-fired a missile off its eastern coast before the announcement of Kim Jong-il's death was made. 
 
 Unnamed government officials in Seoul were quoted as saying they did not believe the launch was linked to the announcement. The South Korean defence ministry has declined to comment. 
 
 Following news of Mr Kim's death, South Korea put its armed forces on high alert and said the country was on a crisis footing. Japan's government convened a special security meeting. 
 
 China - North Korea's closest ally and biggest trading partner - expressed shock at the news of his death and pledged to continue making "active contributions to peace and stability on the Korean peninsula and in this region". 
 
 Asian stock markets fell after the news was announced. 
 
 Crying aloud 
 
 Mr Kim's death was announced in an emotional statement on national television. 
 
 Analysis North Korea has shocked the world by announcing that its leader has died. Kim Jong-il had been presented to his people as a father-figure and demi-god - all-powerful and benevolent. But his tight control of the country, and his creation of a nuclear arsenal, has meant his death has caused political shockwaves around the region too. His presumed successor, Kim Jong-un, is largely unknown outside the secretive state, and countries throughout the region are watching closely for any instability in the transition of power. 
 
 The announcer, wearing black, struggled to keep back the tears as she said he had died of physical and mental over-work. 
 
 The KCNA later reported that he had died of a "severe myocardial infarction along with a heart attack" at 08:30 local time on Saturday (23:30 GMT Friday). 
 
 He had been on a train at the time, for one of his "field guidance" tours, KCNA said. 
 
 The state news agency said a funeral would be held in Pyongyang on 28 December and Kim Jong-un would head the funeral committee. A period of national mourning has been declared from 17 to 29 December. 
 
 Images from inside the secretive state showed people in the streets of Pyongyang weeping at the news of his death. 
 
 Ruling party members in one North Korean county were shown by state TV banging tables and crying out loud, the AFP news agency reports. 
 
 "I can't believe it," a party member named as Kang Tae-Ho was quoted as saying. "How can he go like this? What are we supposed to do?" 
 
 Another, Hong Sun-Ok, said: "He tried so hard to make our lives much better and he just left like this." 
 
 KCNA said people were "convulsing with pain and despair" at their loss, but would unite behind his successor Kim Jong-un. 
 
 "All party members, military men and the public should faithfully follow the leadership of comrade Kim Jong-un and protect and further strengthen the unified front of the party, military and the public," the news agency said. 
 
 Little is known about Kim Jong-un. He was educated in Switzerland, is aged in his late 20s and is believed to be Kim Jong-il's third son - born to Mr Kim's reportedly favourite wife, the late Ko Yong-hui. 
 
 Kim Jong-un was unveiled as his father's likely successor just over a year ago. Many had expected to see this process further consolidated in 2012. 
 
 'Turning point' 
 
 South Korea - which remains technically at war with the north - urged people to "go about their usual economic activities" on Monday, while putting the military on alert. 
 
 President Lee Myung-Bak spoke to US President Barack Obama by telephone and they "agreed to closely co-operate and monitor the situation together", a South Korean presidential spokesman said. 
 
 Reaction from Washington was muted, with the White House saying it was "closely monitoring" reports of the death. 
 
 The US remained "committed to stability on the Korean peninsula, and to the freedom and security of our allies", it said in a statement. 
 
 China said it was "distressed" to hear the news of his death. "We express our grief about this and extend our condolences to the people of North Korea," foreign ministry spokesman Ma Zhaoxu was quoted by Xinhua news agency as saying. 
 
 Analysis Kim Jong-il's death should not have come as a complete surprise to anyone, given his tenuous health. But it is safe to say that the North Koreans would have very much preferred that he lived one more year, so that in 2012, the 100th anniversary of the birth of Kim Il-sung, his father, Kim Jong-il would have been on hand to pay homage to "the Great Leader". Now that lot will fall to Kim Jong-un, Kim Jong-il's youngest son who has been put forward as the natural and fully prepared successor to his father. Will Kim's death aid ties with US? 
 
 Analysts say that with the process of transition from father to son incomplete, Mr Kim's death could herald "very unstable times" in North Korea. 
 
 "We have to be very worried because whenever there is domestic instability North Korea likes to find an external situation to divert the attention away from that - including indulging in provocation," Professor Lee Jung-hoon, specialising in international relations at Yonsei University in Seoul, told the BBC. 
 
 Christopher Hill, former US representative to the six-party talks on North Korea's nuclear programme, said all parties needed to "keep cool heads". 
 
 Britain's Foreign Secretary William Hague said it could be a "turning point" for North Korea to engage more closely with the international community. 
 
 Kim Jong-il inherited the leadership of North Korea from his father Kim Il-sung. 
 
 Shortly after he came to power in 1994, a severe famine caused by ill-judged economic reforms and poor harvests left an estimated two million people dead. 
 
 His regime has been harshly criticised for human rights abuses and is internationally isolated because of its pursuit of nuclear weapons. 
 
 Under Mr Kim's leadership, funds have been channelled to the military and in 2006 North Korea conducted its first nuclear test. It followed that up with a second one three years later. Multinational talks aimed at disarming North Korea have been deadlocked for months. 
 
 He had reportedly been in poor health since suffering a stroke in August 2008.
– Kim Jong Il, North Korea's mercurial and enigmatic leader, has died at the age of 69, according to state television. His death was was announced today by a tearful announcer in black who said he had died from physical and mental over-work while on a train trip to a location outside Pyongyang, Reuters reports. A later report from state-run media said the "Dear Leader" had died of heart failure. Kim, revered as a man of almost superhuman talents by state-run media, but widely mocked in the West, inherited power after his father's death in 1994. His designated successor is believed to be his son, Kim Jong Un, who is still in his 20s. Asian stock markets fell on the news of his death and South Korea placed its military on alert. With the transition to power in North Korea incomplete, "very unstable times" times could lie ahead for the diplomatically isolated nation, an analyst tells the BBC.