Officials are searching for thousands of people missing across wide areas of north-eastern Japan more than a day after a devastating earthquake and tsunami.
The confirmed death toll from Friday's twin disasters is 686, but the government's chief spokesman said it could exceed 1,000. Devastation stretches hundreds of miles along the coast, where thousands of hungry survivors huddle in darkened emergency centres cut off from rescuers and aid.
The scale of destruction is not yet known, but there are grim signs that the death toll could soar. One report said four trains had disappeared and had still not been located. Others said 9,500 people in the coastal town of Minamisanriku were unaccounted for and that at least 200 bodies had washed ashore elsewhere.
Atsushi Ito, an official in Miyagi prefecture, among the worst hit states, could not confirm those figures, noting that with so little access to the area, thousands of people in scores of town could not be contacted or accounted for.
"Our estimates based on reported cases alone suggest that more than 1,000 people have lost their lives in the disaster," said Chief Cabinet Secretary Yukio Edano. "Unfortunately, the actual damage could far exceed that number considering the difficulty assessing the full extent of damage."
Among the most worrying developments was the possible meltdown of a nuclear reactor near the quake's epicentre. Mr Edano said an explosion caused by vented hydrogen gas destroyed the exterior walls of the building where the reactor is, but not the actual metal housing enveloping the reactor. Japan's nuclear safety agency later reported cooling systems had failed at a second reactor in the same complex.
Power was knocked out by the quake in large areas of Japan, which has requested increased energy supplies from Russia, RIA Novosti agency reported.
The concerns about a radiation leak at the nuclear power plant overshadowed the massive tragedy laid out along a 1,300-mile stretch of the coastline where scores of villages, towns and cities were battered by the tsunami, packing 23ft high waves.
It swept inland about six miles in some areas, swallowing boats, homes, cars, trees and everything else. Firefighters have yet to contain a large blaze at the Cosmo Oil refinery in the city of Ichihara.
According to official figures, about 650 people are missing and 1,400 injured. Prime Minister Naoto Kan said 50,000 troops joined rescue and recovery efforts, aided by boats and helicopters. Dozens of countries also offered help.