A 7.4 magnitude earthquake off Japan's Fukushima and Miyagi prefectures has sparked tsunami waves of more than 1m.
The quake struck at about 06:00 local time (21:00 GMT Monday), the Japan Meteorological Agency said.
Residents were told to seek higher ground immediately, with warnings of waves of up to 3m. There were reports of minor injuries and damage.
An earthquake and tsunami struck the same area in 2011 killing more than 18,000 people.
That quake, one of the most powerful ever recorded, also caused a meltdown at the Fukushima nuclear power plant, where a massive clean-up operation is still going on.
Officials have said there is no sign of damage to the plant this time.
The US Geological Survey initially put the magnitude at 7.3 but later downgraded this to 6.9, lower than the number given by the Japanese authorities.
The meteorological agency said the latest tremor was an aftershock of the 2011 quake.
A spokesman quoted by Japan Times said the area was still generating at least one earthquake of 7.0 magnitude or more each year.
The depth of Tuesday's quake was estimated to be 30km (18.6 miles), the JMA said.
Strong tremors could be felt as far away as the capital, Tokyo, 100 miles south of Fukushima prefecture. Buildings in the capital shook for at least 30 seconds.
The BBC's Rupert Wingfield-Hayes in Tokyo says tens of thousands of people have heeded evacuation warnings and headed for higher ground.
Ships could be seen moving away from harbours in Fukushima prefecture and car manufacturer Nissan suspended work at its Fukushima engine factory.
A 1m wave hit the coastline near the Fukushima nuclear power plant, but Cabinet Chief Secretary Yoshihide Suga said at a televised news conference that "there was no problem".
All reactors were shut down in 2011, but cooling is still needed for the used nuclear fuel stored on the site.
Mr Suga said the water cooling system on the third reactor had stopped working, but there were no signs of further damage or abnormalities.
Tokyo Electric Power, which operates the plant, later said it had restarted the cooling system, and reported only small temperature increases, within safety limits.
A wave of 60cm (2ft) arrived in Onahama Port in Fukushima, Japanese broadcaster NHK reported, and another of 90cm in Soma.
Tsunami warnings were downgraded after four hours, but locals were asked to continue evacuating the area and to avoid the coastline.
There so far appears to have been only minimal damage, and our correspondent says tsunami defences rebuilt since 2011 have ensured that waves have not caused flooding nor damage.
More than 18,000 people were killed or are still missing after the 2011 Fukushima quake and tsunami, which devastated a wide area.
The meltdown at the power plant contaminated the surrounding area, displacing at least 100,000 people.