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.