LATEST: Japan is pushing 50,000 rescue staff into quake and tsunami-devastated areas as officials warn they expect the death toll to "rise greatly".
The United States, with almost 50,000 troops stationed in Japan, sent aircraft carriers to waters off the disaster zone as the relief effort gathered pace.
On the east coast of Japan's main island, Honshu, where at least 3,600 houses were destroyed, there were some hope as army helicopters airlifted people off the roof of an elementary school in Watari, Miyagi prefecture.
Miraculously, naval and coastguard choppers rescued 81 people from a ship that had been dragged out to sea by the tsunami.
Meanwhile, Japan is evacuating tens of thousands of residents from around two nuclear power plants.
Officials today warned of a possible radiation leak as authorities battled to contain rising pressure at the plants 240km north of Tokyo.
Tokyo Electric Power Co said it had begun to release pressure at its two nuclear power plants in Fukushima.
Altogether, five nuclear reactor units - two at the Fukushima No. 1 plant and three at nearby Fukushima No. 2 plant - are in a state of emergency. All five units were shut down after the massive quake Friday.
Underscoring grave concerns about the Fukushima plant, the US air force delivered coolant to avert a rise in the temperature of its nuclear rods but officials said a leak was still possible because pressure would have to be released.
Kyodo news agency reported that authorities had begun evacuating about 20,000 people from the vicinity of one of the plants.
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A pregnant New Zealander living nearby said she feared one of the plants would explode.
Jayne Nakata - Jayne Lark until she married a Japanese man - said one of the plants was about 50km from her home.
"If there was a large explosion we would be affected here,'' she said today.
Radiation levels inside the plant had increased 1000 times above the norm, although authorities said levels outside the facility's gates were only eight times above normal, which meant there was "no immediate health hazard''.
While some radiation leakage could be expected, Naoto Sekimura, a professor at the University of Tokyo, said a major radioactive disaster was not likely.
''Even in the worst-case scenario, that would mean some radioactive leakage and equipment damage, but not an explosion. If venting is done carefully, there will be little leakage. Certainly not beyond the 3km radius,'' he said.
The unfolding disaster prompted offers of search and rescue help from 45 countries, including New Zealand.
Prime Minister John Key said 48 New Zealand search and rescue staff would be on the ground in Japan by the end of Sunday.
China said rescuers were ready to help with quake relief while President Barack Obama told Japanese Prime Minister Naoto Kan the US would assist in any way.
Japanese politicians pushed for an emergency budget to fund relief efforts after Prime Minister Naoto Kan asked them to "save the country," Kyodo news agency reported. Japan is already the most heavily indebted major economy in the world, meaning any funding efforts would be closely scrutinised by financial markets.
Domestic media said the death toll was expected to exceed 1300, most of whom appeared to have drowned by churning waters after the mid-afternoon earthquake.
FIRES ACROSS THE COAST
The quake sparked at least 80 fires in cities and towns along the coast, Kyodo said.
Power plants and oil refineries were shut down and one refinery was ablaze. Television footage showed an intense fire in the waterfront area near Sendai.
Auto plants, electronics factories and refineries shut, roads buckled and power to millions of homes and businesses was knocked out. Several airports, including Tokyo's Narita, were closed and rail services halted. All ports were shut.
Warnings were issued for countries to the west of Japan and across the Pacific as far away as Colombia and Peru, but the tsunami dissipated as it sped across the ocean and the worst fears in the Americas were not realised.
BIGGEST OF ALL
The quake surpasses the Great Kanto quake of September 1, 1923, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.
The 1995 Kobe quake caused $100 billion in damage and was the most expensive natural disaster in history. Economic damage from the 2004 Indian Ocean tsunami was estimated at about $10 billion.
Earthquakes are common in Japan, one of the world's most seismically active areas.
- Reuters, AP and NZPA
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