TOKYO — The number of missing and feared dead in Japan's epic earthquake soared to more than 1,800 by early Sunday as a reeling nation struggled to contain an unprecedented nuclear crisis, pluck people in tsunami-inundated areas to safety, quell raging blazes and provide succor to hundreds of thousands of frightened people left homeless and dazed.
As the second full post-quake day dawned Sunday, authorities said about 400,000 people had been forced to flee the quake's giant swath of destruction — more than a quarter of them refugees from the area surrounding the Fukushima nuclear plant, 150 miles north of Tokyo. The crisis intensified as officials reported three of the Fukushima complex's six reactors were in trouble, and emergency measures were being taken to cool them.
Dozens of people were believed to have been exposed to elevated levels of radiation, and officials sought to reassure a frightened public that the radiation leak was under control. Cesium and iodine, byproducts of nuclear fission, were detected around the plant in what could rank as the worst atomic incident in Japan's roughly half-century of nuclear power generation.
With punishing aftershocks continuing to jolt the quake zone, the Japanese military was mobilizing 50,000 of its personnel, together with ships and planes, to aid in a rescue effort that has swiftly turned into a deadly race against time. In a country where every modern convenience has long extended into even remote areas, the basics of daily survival — food, water, power — were unaccustomedly threatened.
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Even in Tokyo, where quake damage was limited, the rhythms of a normally throbbing metropolis were stilled. In many central districts, the trademark neon blaze of illumination was absent on streets that were eerily deserted. The subway system was running again, if sporadically, but on a Saturday evening, when its jolting cars would normally be packed with passengers, some slid through stations all but empty, like ghost trains.
Even Tokyo Disneyland said it would be shuttered for at least 10 days.
As of early Sunday, the confirmed death toll stood at 687, the Kyodo news agency reported, citing police figures. That did not include another 200 to 300 unidentified corpses — mostly tsunami victims — that had been transported to Sendai, the hardest-hit large city.
"It is believed that more than 1,000 people have lost their lives," said Yukio Edano, the chief Cabinet secretary.
But assessments of the disaster were far from certain. Although the official missing tally stood at 650, in Miyagi prefecture north of Tokyo, officials said Saturday night that there had been no contact with about 10,000 people in the small town of Minamisanriku, more than half its population.
Some people decided to try to get more information about missing relatives on their own. When Tokyo office worker Yuki Ochiai, 25, heard that three-quarters of the 24,000 people living in the northern coastal town of Rikuzentakata were unaccounted for, he headed north to find out the fate of family living there. He rode his motorcycle because roads were impassable by car.
"This is crazy," he said as he stopped to buy water and gas outside of Fukushima, still far from his destination. "One place. The other 18,000 people, they don't know where they are?"
Japan's peacetime military, the Self-Defense Forces, was mobilizing a relief-and-rescue force of 50,000, the defense ministry said, including a special unit detailed to help nuclear evacuees. Nearly 200 aircraft and 45 ships were en route or in the tsunami zone, according to the ministry.
The U.S. military, whose bases are sometimes an irritant to local residents, was aiding in the relief effort as well. The Americans said there were no injuries or serious damage at any of their bases, and Japanese Defense Minister Toshimi Kitazawa said the U.S. 7th Fleet would be providing search-and-rescue help along Japan's northeastern Pacific coast.
The task was a daunting one. Whole communities were still under water in the wake of the massive tsunami unleashed by the 8.9 magnitude quake, the most powerful in Japan's recorded history. Those included Rikuzentakata and the smaller town of Miyako, both in Iwate prefecture.
Despite Japan's much-vaunted earthquake engineering, which saved countless lives, at least 3,400 buildings were known to have been destroyed by the quake and by blazes, Kyodo news agency said, citing the national fire agency. But that figure too could grow exponentially. In the town of Kesennuma, in hard-hit Miyagi prefecture, fires merged into a mega-blaze stretching for more than half a mile. The welfare ministry said 171 "welfare facilities," such as nursing homes, had suffered damage.
Lending critical urgency to the rescue effort, nearly 6 million homes were reported to be without electricity, and more than 1 million lacked water.
Quake survivors were further terrorized by aftershocks, one of which was measured at magnitude of 6.7.
The quake's economic jolt also has yet to be fully assessed. Manufacturing heavyweights such as Toyota, Nissan and Honda said production at plants well outside the quake zone were expected to be suspended on Monday because of the difficulty in obtaining parts.
Flights resumed at Tokyo's Narita airport, one of the world's busiest, but its usually bustling terminals were quiet, and hundreds of domestic flights were canceled. Piles of neatly stacked sleeping bags stood as testament to the long wait endured by many to either catch planes out or find a way into the city aboard slow-moving local trains instead of the usual speedy express. Service on the country's iconic shinkansen, or bullet train, remained sharply curtailed. Nine major expressways were shut down because of structural fears.
At the crippled nuclear plant in Fukushima, authorities were still were unable to explain why excess levels of radiation were detected outside the complex's grounds. An explosion was heard near the plant's No. 1 reactor about 3:30 p.m. Saturday, and plumes of white smoke could be seen.
Edano, the Cabinet secretary, said the blast was caused by a buildup of hydrogen in the cooling system and described the evacuation of more than 100,000 people across a 12-mile area as a "precaution."
Japan's nuclear and industrial safety agency said more than 70 people were believed to have been exposed to elevated radiation levels, the Asahi Shimbun newspaper reported. Most were waiting to be airlifted from a field at the local high school in the town of Futaba, near Fukushima.
On Sunday, the cooling system at a third reactor at the Fukushima plant was reported to be malfunctioning as well. Edano said steam was being vented and water added, "and those measures should stabilize the situation."
The International Atomic Energy Agency in Vienna said it was told by Japanese officials that they would distribute iodine tablet to residents nearby. Iodine is known to protect against thyroid cancer that can develop from radiation poisoning.
The biggest concern about the plant is the possibility of the core overheating and nuclear material escaping from the containment vessel.
When the earthquake struck Friday afternoon, the reactors automatically shut down as they were supposed to, a safety measure built into the design. But cooling systems — which were supposed to remain on — apparently failed because of the low electrical power.
Four backup diesel generators to supply emergency power also failed.
On Saturday, officials said that the plant's engineers used seawater in an attempt to cool the reactor. They released steam containing low levels of radiation as an emergency cooling measure.
Japan's heavy dependence on nuclear power — which supplies 30 percent of its energy — makes it even more vulnerable in an earthquake.
"Japan is an earthquake-prone archipelago, and lining its waterfront are 54 nuclear plants. It's been like a suicide bomber wearing grenades around his belt," said Katsuhiko Ishibashi, a professor emeritus at Kobe University.
Since Friday's quake, 11 of the country's reactors have been shut down, sharply reducing the electrical supply available in the country.
———(Staff writers Demick reported from Fukushima prefecture, Magnier from Koriyama and King from Tokyo. Special correspondents Yuriko Nagano and Kenji Hall contributed to this report.)