An earthquake with a preliminary magnitude of 6.2 jolted northern Japan on Sunday, the Japan Meteorological Agency said, though there were no reports of damage and nuclear facilities in the area were unaffected.
The quake, at 12:33 pm (0333 GMT), was also felt in Tokyo.
The focus of the tremor was 40 km (25 miles) below sea level off the east coast of Fukushima prefecture, on Japan's main island of Honshu, about 240 km (150 miles) northeast of Tokyo, the Japan Meteorological Agency said.
No tsunami warning was issued.
The US Geological Survey reported the quake's magnitude at 6.1 and put it at a shallower 7 km depth.
Tokyo Electric Power Co's Fukushima No.1 and No.2 nuclear power plants were operating normally after the quake, a company spokesman said.
Sendai airport in neighbouring Miyagi prefecture halted flights briefly to check the runway before resuming operations, national broadcaster NHK said.
Earthquakes are common in Japan, one of the world's most seismically active areas. The country accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.
In October 2004, an earthquake with a magnitude of 6.8 struck the Niigata region in northern Japan, killing 65 people and injuring more than 3,000.
That was the deadliest quake since a magnitude 7.3 tremor hit the city of Kobe in 1995, killing more than 6,400.