An earthquake with a magnitude of 6.9 hit off northeastern Japan, the country's Meteorological Agency said.
The US Geological Survey had a preliminary magnitude of 7.3, but then downgraded it to 6.9.
It issued tsunami warnings for much of the nation's northern Pacific coast. The epicentre of the earthquake was felt in Tokyo, off the coast of Fukushima prefecture at a depth of about 10km, according to the agency.
The warning has been issued for waves of up to three metres. People by the coast are being told to evacuate immediately.
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There were no initial reports of damage or injury.
Fukushima prefecture is north of Tokyo and home to the nuclear power plant destroyed by a huge tsunami after an offshore earthquake in 2011.
Tohoku Electric said it had found no abnormalities at its Onagawa nuclear power plant after the earthquake. All nuclear plants on the coast threatened by the tsunami are shut down in the wake of the Fukushima disaster.
Just two reactors are operating in Japan - both in the southwest of the country.
Japan is one of the world's most seismically active places: earthquakes there account for around 20 per cent of the world's earthquakes of magnitude 6 or greater.
Earlier this year, Sony said earthquakes in Kumamoto were among the reasons for a 48 per cent fell in operating profit in the second quarter to the end of September.
In the immediate aftermath of the earthquake news, the Nikkei futures turned negative, while the dollar also slumped against the yen, though it quickly rallied.
Yen appreciation may seem counter-intuitive but in 2011 yen strengthened on expectations of repatriation flows after earthquake— LiveSquawk (@LiveSquawk) November 21, 2016