A strong earthquake shook the northeast of Japan and a tsunami warning was issued for the coast already devastated by last month's massive quake and the tsunami that crippled a nuclear power plant.
Officials said Thursday's quake was a 7.4-magnitude and hit 40km under the water and off the coast of Miyagi prefecture.
No damage from the quake was detected at the Fukushima Daiichi nuclear power plant and
NHK TV said workers had been evacuated without reports of any injuries.There were no immediate reports of injuries or damage elsewhere but people in areas covered by the tsunami warning should evacuate to higher ground, Japan's NHK public television said.
Japan is struggling to bring the Fukushima Daiichi plant under control after the March 11 quake and tsunami, which killed, or left missing, about 28,000 people.
Japan's neighbours have sounded increasingly alarmed over the risk of radiation from the plant, while tourists are staying away in what should be the peak season, and the country seeks ways to cut power use.
The world's worst nuclear disaster in 25 years is also raising concern over safety in the United States, which has more atomic reactors than any other country, especially at one plant which is similar to the one in Fukushima wrecked by last month's 9.0 magnitude earthquake and tsunami.
Engineers, who sealed a leak this week that had allowed highly radioactive water into the sea, are pumping nitrogen into one reactor to prevent the risk of a hydrogen gas explosion, and want to start the process in another two reactors.
Operator Tokyo Electric Power Co (TEPCO) said late on Thursday it did not expect it would have to dump any more contaminated water into the ocean after Saturday.
Earlier, TEPCO said the chance of a repeat of the gas explosions that damaged two reactors in the first days of the disaster was "extremely small".
But as engineers battle multiple crises - some the result of efforts to try to cool reactors - officials admit it could take months to bring the reactors under control and years to clear up the toxic mess left behind at the plant 240km north of Tokyo.
