A Japanese government spokesman has urged for calm following an explosion at one of two nuclear plants damaged in Friday's massive earthquake.
Japanese Chief Cabinet Secretary Yukio Edano says authorities are monitoring radiation levels at Fukushima, where smoke could be seen billowing out of the nuclear plant complex. Japanese media say radiation levels are more than eight times normal outside the plant.
He urged people to follow earlier orders to evacuate the area 10 kilometers around the plant.
Before the explosion occurred, authorities said radioactive material had been found outside one of the plant's reactors, which had lost power and cooling abilities following the magnitude 8.9 quake and tsunami.
Prime Minister Naoto Kan said 50,000 troops would join rescue and recovery efforts across the country.
Japanese media report more than 1,200 people are dead or missing.
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 provided by AP, AFP and Reuters.