As aftershocks to the 8.9 magnitude quake continued to strike, an atomic emergency was declared and tens of thousands of people were ordered to evacuate after cooling systems failure caused two power plants to overheat.
There were reports on an explosion at the Daichi 1 plant, about 150 miles northeast of Tokyo. AFP said smoke was billowing from the building. "Several workers were injured and radioactivity rose 20-fold outside," it said.
"We are not in a situation in which residents face health damage," Chief Cabinet Secretary Yukio Edano told reporters.
However a total of 45,000 people living within a seven mile radius of the power plant and within two miles of a second reactor, were told to leave their homes.
"An unchecked rise in temperature could cause the core to essentially turn into a molten mass that could burn through the reactor vessel," political risk information service Stratfor said in a report quoted by Reuters.
The Telegraph newspaper quoted Mark Hibbs, a nuclear expert at the Carnegie Endowment for International Peace, predicting meltdown. “What we’re seeing, barring any information from the Japanese that they have it under control, is that we’re headed in that direction,” he said.
Media reports estimated at least 1,300 people died in the earthquake and the tsunami which engulfed vast tracts of farmland and entire towns as it swept inland. The death toll was expected to rise as rescuers reached the worst-hit areas.
The scale of the quake, the largest in Japan since records began 140 years ago, triggered tsunami alerts and evacuations around the Pacific rim. Most alerts were later scaled back as the resulting waves caused minimal damage.
"Waves as high as six feet crashed into South America into early Saturday— in some cases sending the Pacific surging into streets —- after coastal dwellers rushed to close ports and schools and evacuated several hundred thousand people," The Associated Press said. CNN reported one death in California.
Around Sendai, the Japanese city closest to the quake's epicenter, efforts to reach disaster survivors were underway. Teams used heavy machinery to dig out 13 people trapped when their homes collapsed, CNN said.
"Military choppers flew over the affected areas and plucked people from rooftops. In some cases, rescuers trudged along muddy waters, carrying victims on their backs. Weary, mud-spattered survivors wandered through streets filled with crumpled cars and other debris," it said.
Six million homes — more than 10 percent of Japan's population — were without electricity following the disaster, CNN quoted Japan's ambassador to the United States saying.
More than 215,000 people were being put up in emergency shelters in the country's northeast, but the number of people left homeless was expected to be much higher, Sky News said.
Japan has mobilized 50,000 military and other rescue personnel, drafting its entire Self Defense Force to help reach those affected as Prime Minister Naoto Kan warned speed was imperative, AFP said.
"I realized the huge extent of the tsunami damage," he said, flying over affected areas in a helicopter. "What used to be residential areas were mostly swept away in many coastal areas and fires are still blazing there."
Sky reported that a ship feared lost after the tsunami swept it out to sea had been found by naval and coast guard helicopters and all 81 people on board were airlifted to safety.
The United States said it was re-routing several Navy vessels towards Japan and preparing helicopters and planes for humanitarian missions, the Washington Post reported.
Two aircraft carriers — the USS George Washington, based near Tokyo, and the USS Ronald Reagan, which was on its way to South Korea — were said to be en route to the disaster zone.
"This is a potentially catastrophic disaster, and the images of destruction and flooding coming out of Japan are simply heartbreaking," President Barack Obama told reporters on Friday.