A strong earthquake with a preliminary magnitude of 6.6 jolted northern Japan today, seismologists said, shaking buildings in the capital Tokyo some 240 km away.
There were no reports of injuries or damage and no tsunami warning was issued. The magnitude of the quake, which struck just after 5pm local time, was measured at 6.6 by the US Geological Survey and the Japan Meteorological Agency (JMA).
The epicentre was about 40 km (25 miles) beneath the ocean off Honshu, Japan's main island, the JMA said. Tokyo Electric Power Company (TEPCO) said its two nuclear power plants in the region were operating normally.
Tohoku Electric Power Co said operations at its Onagawa and Higashidori nuclear power plants were also normal.
Operations at Fujitsu Ltd's semiconductor plant in Fukushima prefecture, in northeast Japan, were also not affected by the quake, an official at Japan's top IT services firm said.
Public broadcaster NHK said a bullet train in the area automatically halted for a brief time but soon resumed operating.
Expressways were closed for checks and police and fire departments were quoted as saying there were no reports of damage after the quake, NHK said.
Japan is one of the world's most earthquake-prone countries, with a tremor occurring at least every five minutes.