TOKYO-- The Japanese government on Friday told thousands of residents living by a nuclear plant in Fukushima to evacuate after the biggest earthquake in Japan's history hit the region.

Earlier the government declared an atomic power emergency but said no radiation leaks were detected among its reactors after an 8.9-magnitude earthquake struck Friday, triggering a huge tsunami.

The government issued the advice for nearly 6,000 residents living within a three-kilometer (1.86-mile) radius of the Fukushima No. 1 plant, operated by Tokyo Electric Power Co.

The plant had shut down but a reactor cooling system failure had led to the evacuation instruction.

Japan's military was sending its chemical corps and an aircraft on a "fact finding mission" near the nuclear plant, Kyodo news reported.

"An instruction has been issued to residents within a radius of three kilometers to evacuate and those within three to 10 kilometers to stay indoors," said Chief Cabinet Secretary Yukio Edano.

"This is an evacuation instruction just for precaution, and there has been no radiation leak from the reactor."

Prime Minister Naoto Kan had earlier said no radiation leaks had been detected from Japan's nuclear power stations after the massive quake struck the country.

A fire broke out in the turbine building of Onagawa nuclear plant in Miyagi Prefecture, but operator Tohoku Electric Power said there were no indications of a radioactive leak, Kyodo News reported.

Miyagi prefecture was one of the areas worst hit by the tsunami.

Around 4.4 million households were without power in northeastern Japan, according to Tohoku Electric.