A magnitude 5.5 earthquake hit eastern Japan on Saturday morning, rocking buildings in Tokyo.
The US Geological Survey said the quake occurred at 7.37am local time in Ibaraki prefecture, north of the capital, at a depth of 59km.
The quake lasted about 30 seconds and was felt by many people in Tokyo.
NHK says there was no threat of a tsunami.
Bullet trains connecting Tokyo with northern Japan were briefly suspended.
The Tokyo Electric Power Company, which operates the wrecked Fukushima nuclear plant 220km northeast of Tokyo, says there was no apparent impact from the quake.
