Sendai , Japan ( CNN ) -- In a nation already besieged with grief over mounting casualties , fears of possible radiation and the threat of more earthquakes , the nightmare grew for Japanese residents Monday as thousands of bodies reportedly surfaced and a government official confirmed another explosion at a nuclear reactor building . The official death toll from the epic quake and devastating tsunami that hit Japan four days ago reached 1,720 on Monday . But the numbers did not take into account the 2,000 bodies that Japan 's Kyodo news agency said had been found in the hard-hit Miyagi Prefecture on Japan 's northeast coast . Meanwhile , fresh white smoke rose again Monday from the Fukushima Daiichi nuclear power plant , caused by an explosion at a building tied to the facility 's No . 3 reactor . A similar explosion occurred two days earlier at the plant 's No . 1 reactor building . Chief Cabinet Secretary Yukio Edano said Monday that the head of the nuclear plant reported the container vessel surrounding the No . 3 reactor remained intact . Yukio said in a news conference that there is little possibility that radioactive material was released into the air , NHK said . The explosion was likely caused by a combination of oxygen and hydrogen igniting , according to Japanese public broadcaster NHK . `` We are now collecting information on the concentration of radiation , '' Edano said . The quake and tsunami disabled the coolant systems at Fukushima Daiichi , which is about 260 km ( 160 miles ) north of Tokyo . Japanese authorities have said there is a `` possibility '' that a meltdown has occurred in the damaged reactors , but said that there were no indications of dangerously high radiation levels in the atmosphere . Still , the government has evacuated more than 200,000 residents from homes close to the plant and tested 160 people for radiation exposure on Sunday , authorities said . Workers flooded two of the six reactors at the Fukushima Daiichi plant in a last-ditch attempt to head off a catastrophic meltdown of the reactor cores . In Miyagi Prefecture , rescue workers sifted through mountains of debris as hope for survivors appeared to dim . The town of Minami Sanriku -- about 5 kilometers from the Pacific Ocean -- morphed into a massive pile of wood that used to house some 20,000 residents . An eerie silence fell across town as emergency rescue officials said they do n't think anyone was still alive under the rubble . About half of Minami Sanriku 's population was unaccounted for . So far , about 15,000 people have been rescued , the Kyodo News Agency reported Monday , citing Kan. Japanese troops went door-to-door in the city of Ishinomaki , hoping to find survivors -- but found mostly the bodies of elderly residents . In the area of Sendai , where houses and buildings disintegrated into rushing water within seconds , solemn reisdents waited in lines that stretches blocks ore kilometers for food , water and gas . Despite the devastation surrounding them , the crowds appeared calm and orderly . But more destruction could still come . There 's a high chance of a magnitude-7.0 quake or above in the next three days because of increased tectonic activity , the earthquake prediction department chief for the Japan Meteorological Agency said Sunday . The U.S. Geological Survey reported scores of such aftershocks . More than two dozen were greater than magnitude 6 , the size of the quake that severely damaged Christchurch , New Zealand last month , the agency said . On Sunday , the country 's prime minister called on people to pull together and face sacrifices . `` In the 65 years after the end of World War II , this is the toughest and the most difficult crisis for Japan , '' Prime Minister Naoto Kan told reporters at a televised news conference . `` We Japanese had a lot of difficulties in the past , but we were able to overcome those difficulties to reach this peaceful and prosperous society we have been able to build , '' Kan said . `` So with regard to the earthquake and tsunami , I am confident that the Japanese people can be united to work together . '' The cooperation Kan called for will include accepting rolling blackouts in some areas to preserve electricity as emergency workers try to repair power plants damaged by the quake . About 2.5 million households , just over 4 % of the total in Japan , were without electricity Sunday , said Ichiro Fujisaki , the nation 's U.S. ambassador . Landmarks such as Tokyo Tower and the capital 's Rainbow Bridge went dark in an effort to conserve energy . Japanese officials raised the quake 's magnitude to 9.0 on Sunday , but the USGS kept its magnitude at 8.9 . At least 48 other countries and the European Union have offered relief . The nuclear-powered aircraft carrier USS Ronald Reagan arrived off Japan 's coast Sunday to support Japanese forces in disaster relief operations , the U.S. Department of Defense said in a statement . Friday 's quake is the strongest in recorded history to hit Japan , according to USGS records that date to 1900 . The world 's largest recorded quake took place in Chile on May 22 , 1960 , with a magnitude of 9.5 , the agency said . CNN 's Gary Tuchman , Anna Coren , Kyung Lah , Paula Hancocks , Brian Walker , Kevin Voigt and Sean Morris contributed to this report .
Official : There is little possibility that radioactive material was released in the air . About 2,000 bodies were found Monday in Miyagi prefecture . The death toll reached 1,720 on Monday , though the number is expected to rise . There 's a high chance of a second quake or above in the coming days , an official said .