Vehicles are piled up in Kesennuma, Japan, on Saturday, a day after a strong earthquake triggered a devastating tsunami on Japan's east coast that swept away cars, houses and people. Nearly 600 people are confirmed dead, although officials say that number is likely to rise.

IWAKI, Japan — An explosion at a nuclear power station Saturday destroyed a building housing the reactor, but a radiation leak was decreasing despite fears of a meltdown from damage caused by a powerful earthquake and tsunami, officials said.

Government spokesman Yukio Edano said the explosion destroyed the exterior walls of the building where the reactor is placed, but not the actual metal housing enveloping the reactor.

That was welcome news for a country suffering from Friday's double disaster that pulverized the northeastern coast, leaving at least 574 people dead by official count.

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. Local media reports said at least 1,300 people may have been killed.

Edano said the radiation around the Fukushima Dai-ichi plant had not risen after the blast, but had in fact decreased. He did not say why that was so. The pressure in the reactor also was decreasing after the blast, he said.

The explosion was preceded by a puff of white smoke that gathered intensity until it became a huge cloud enveloping the entire facility in Fukushima, 20 miles from Iwaki. After the explosion, the walls of the building crumbled, leaving only a skeletal metal frame.

Tokyo Power Electric, the utility that runs the Fukushima Dai-ichi plant, said four workers suffered fractures and bruises and were being treated at a hospital.

“We have confirmed that the walls of this building were what exploded, and it was not the reactor's container that exploded,” said Edano.

The trouble began at the plant's Unit 1 after the massive 8.9-magnitude earthquake and the tsunami it spawned knocked out power there, depriving it of its cooling system.

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 23-foot high waves.