The Fukushima nuclear plant was not damaged in a 7.1 magnitude earthquake which hit the region yesterday, an operator has said.
He said there had been no spike in radiation levels either, despite the quake triggering a small tsunami.
The quake struck about 370km into the ocean east of Japan.
The operator of the Fukushima nuclear plant has ordered workers near the coast to move to higher ground after a 7.6 magnitude earthquake, Japanese broadcaster NHK reported.
Japan's emergency agencies have declared a tsunami warning for the region that includes the crippled nuclear site.
All but two of Japan's 50 reactors have been offline since a magnitude-9.0 earthquake in March 2011 triggered a tsunami which led to massive radiation leaks at the plant 160 miles northeast of Tokyo.
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The US Pacific Tsunami warning centre said there was no widespread tsunami threat after the earthquake off the coast of Japan.
A powerful 7.6 magnitude earthquake has been recorded 231 miles east of Japan's Honshu island, the US Geological Survey said.
The Japanese weather agency issued a yellow warning for a 1m tsunami in Japan's Fukushima region, due to hit the coast at 6.42pm UK time.