Japan has declared states of emergency at two nuclear plants damaged by Friday's massive earthquake along the country's northeastern coast.
Officials said the 8.9 magnitude quake and subsequent tsunami knocked power out and caused cooling systems to fail at two plants in Fukushima. They warned of radiation leaks as steam was vented from reactors in an effort to relieve growing pressure.
Japanese officials said Saturday the venting would not pose a major safety risk to the public, although authorities ordered people living around the plants to evacuate.
Strong aftershocks rocked Japan as Japanese troops and helicopters worked Saturday to rescue people stranded by the tsunami. More than 1,000 people are feared dead.
Entire villages were washed away Friday by waves as high as 10 meters that carried vehicles, buildings and debris several kilometers inland.
The earthquake and tsunami damaged highways and other infrastructure, further hampering rescuers' efforts to reach people stranded on their roofs and trapped in affected areas.
Japan's Tepco electric company is warning of massive power outages in the coming days across large areas of the country.
Japanese authorities said 200 to 300 bodies have been found in Sendai, the city closest to the quake, which was the most powerful on record to hit Japan and the world's fifth largest in more than a century. They say 700 people are missing and 1,000 people have been injured.
Northeast of Sendai, fires raged through the night Friday in Kesennuma, a town of 70,000 people. A large fire also erupted at an oil refinery in Ichihara, near Tokyo.
In Tokyo, the quake forced a suspension of all train and subway services, leaving millions of people stranded. Several airports were also closed, but some, including Tokyo's Narita have reopened.
Some information for this report was provided by AP, AFP and Reuters.