An explosion at a nuclear power plant in Japan's eastern coast did not take place at the critically important reactor, but officials have nonetheless expanded an evacuation area for residents from about 6 miles to 12 miles.

An explosion at the Fukushima Daiichi No. 1 nuclear power plant on Saturday did not occur at its No. 1 reactor, government spokesman Yukio Edano said, according to Kyodo News.

The plant is adjacent to the shore about 150 miles northeast of Tokyo and about 70 miles south of Sendai along the eastern coast of Honshu, Japan's largest Island.

As a precaution, officials have increased the evacuation area from Fukushima No. 1 and No. from 10 kilometers to 20 km (12.4 miles), Kyodo News reported.

The explosion observed at the plant at 3:36 p.m. local time blew off the roof and walls of the building housing the reactor's container. He said there had been no serious damage to the steel container or the reactor.

Tokyo Electric Power Co. said there is no damage to the steel container housing the reactor, according to the report.

The explosion took place when vapor from the container turned into hydrogen and mixed with outside hydrogen, Edano said.