Blast at Japan nuke plant; thousands missing.

    Blast at Japan nuke plant; thousands missing.

IWAKI, Japan – An explosion shattered a building housing a nuclear reactor Saturday, amid fears of a meltdown, while across wide swaths of northeastern Japan officials searched for thousands of people missing more than a day after a devastating earthquake and tsunami.

The confirmed death toll from Friday's twin disasters was 686, but the government's chief spokesman said it could exceed 1,000. Devastation stretched hundreds of miles (kilometers) along the coast, where thousands of hungry survivors huddled in darkened emergency centers cut off from rescuers, electricity and aid.

The scale of destruction was not yet known, but there were grim signs that the death toll could soar. One report said four whole trains had disappeared Friday and still not been located. Others said 9,500 people in one coastal town 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," Chief Cabinet Secretary Yukio Edano said. "Unfortunately, the actual damage could far exceed that number considering the difficulty assessing the full extent of damage."

Among the most worrying developments was concerns that a nuclear reacter could melt down. Edano said Saturdya's explosion was caused by vented hydrogen gas and destroyed the exterior walls of the building where the reactor is, but not the actual metal housing enveloping the reactor.

Edano said the radiation around the Fukushima Dai-ichi plant had not risen after the blast, but had in fact decreased.

Three people being evacuated from an area near the plant have been exposed to radiation, Yoshinori Baba, a Fukushima prefectural disaster official, confirmed. But he said they showed no signs of illness.

Virtually any increase in ambient radiation can raise long-term cancer rates, and authorities were planning to distribute iodine, which helps protect against thyroid cancer.

Authorities have also evacuated people from a 12-mile (20-kilometer) radius around the reactor.

Blast at Japan nuke plant; thousands missing.