Japan's government spokesman says the metal container sheltering a nuclear reactor was not affected by an explosion that destroyed the building it's in.
Yukio Edano says the radiation around the plant did not rise after the blast but instead is decreasing. He added that pressure in the reactor was also decreasing.
Pressure and heat have been building at the nuclear reactor since an earthquake and tsunami Friday caused its cooling system to fail.
An explosion Saturday blew out the walls of the building housing the reactor. The government has ordered people within a 12-mile (20-kilometer) radius of the plant in Fukushima to evacuate the area.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
An explosion at a nuclear power station Saturday destroyed a building housing the reactor amid fears that it could melt down after being hit by a powerful earthquake and tsunami.
Large amounts of radiation were spewing out and the evacuation area around the plant was expanded but officials did not know how dangerous the leak was to people. Shinji Kinjo, a spokesman for the Japanese nuclear agency, could not say how much radiation was in the atmosphere or how hot the reactor was following the failure of its cooling system.
Friday's double disaster, which pulverized Japan's northeastern coast, has left 574 people dead by official count, although local media reports said at least 1,300 people may have been killed.
Tokyo Power Electric Co., the utility that runs the Fukushima Dai-ichi plant, said four workers had suffered fractures and bruises and were being treated at a hospital. A nuclear expert said a meltdown may not pose widespread danger.