The estimated death toll in Japan's quake and tsunami jumped to more than 10,000 today as scientists battled to stop nuclear meltdowns at two reactors 150 miles north of Tokyo.
The crisis is now officially the world's worst nuclear accident for 25 years.
The head of police in Miyagi prefecture, one of the worst-hit coastal areas, said 10,000 people could be dead in the district, which includes the ruined city of Sendai. Casualties in other areas will push the number higher.
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But the rescue and recovery operations were overshadowed by dangerous developments at no fewer than five nuclear reactors along Japan's tsunami-ravaged northeast coast.
Two of the reactors were feared to be facing a meltdown and cooling systems at three others were failing.
At the Fukushima Daiichi number 1 reactor, engineers reported pumping seawater and boric acid into the vessel holding atomic fuel rods to stop the chain reaction.
Thirty tons an hour were flowing into the crippled reactor through fire appliance pumps.
Officials said radiation levels are above safety limits around the plant but pose no immediate risk to humans.
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An explosion blew apart the building containing the reactor on Saturday but officials say the strengthened reactor core was undamaged.
However engineers were also fighting a likely meltdown at the number 3 reactor in the same plant, where fuel rods may have been damaged.
Japan's Chief Cabinet Secretary, Yukio Edano, warned there could be another explosion at the number 3 reactor as gases were vented and seawater pumped in.
Cooling systems at three other reactors were failing, the operating company reported, raising the risk of a sequence of crises.
More than 300,000 residents have been evacuated from the area around the Fukushima plant.
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Japanese media said up to 190 people were contaminated by radiation and were receiving precautionary medical treatment. They included 19 hospital staff.
Meanwhile the Japanese government has launched a huge rescue and recovery operation using 100,000 troops of the Self-Defence Forces and setting up a co-ordinated command centre at the stricken city of Sendai.
"Saving lives is still the top priority," Prime Minister Naoto Kan said on Sunday.
Rescuers are already finding the bodies of elderly residents and there are fears that cold rain and snow forecast for coming days will reduce the chances of survival.
One woman of 60, Yukiko Saichi, told Japanese broadcaster NHK she and her husband clung to a tree as they were swept away by the tsunami and were rescued by a military helicopter.
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American air, land and naval forces were also swinging into action from bases in Japan and across the Pacific.
An initial flight of helicopters set off for Miyagi prefecture carrying aid and the aircraft carrier USS Ronald Reagan has arrived on station off Japan.
Japanese scientists, meanwhile, have recalculated the strength of Friday's undersea earthquake at 9.0, up from 8.9, making it the most powerful on record to hit Japan.
It had almost 1,450 times the destructive force of the quake that wrecked the city of Kobe in 1995.
Tokyo and other major cities are now bracing for electricity blackouts as power companies try to allocate resources.
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The impact on Japan's economy is expected to be significant. The Bank of Japan is preparing to take unspecified steps to restore confidence and ensure stability when markets open on Monday.
Dealers expect the yen to rise as companies and insurers bring money home to pay liabilities.
The disaster has also led to falls in the prices of oil, metals and grains as traders expect lower demand from the world's third largest economy.