A magnitude 6.8 earthquake off the Japanese coast rattled Tokyo early Wednesday, seismologists and national television said.
There were no immediate reports of injuries or damage, though the quake woke up some residents of the capital, public broadcaster NHK said. No tsunami warning had been issued, it added.
The epicenter of the quake that struck at 01:45 (16:45 GMT) was offshore, 161 kilometers (100 miles) northeast of Tokyo and at a depth of 40 kilometers underwater, according to the U.S. Geological Survey.
NHK reported that a second quake hit in the same area about half an hour later with a magnitude of 5.3 in the Richter scale.
However, the broadcaster reported that power lines and communications were running normally and no injuries or minor damage had been reported. An hour later, regularly scheduled programming had resumed.
Japan is one of the most earthquake-prone countries in the world, although Tokyo has not been hit with a major quake since the 1923 Great Kanto Earthquake killed 140,000 people.
An earthquake of that size, about a magnitude 8, occurs once every 200 to 300 years.