A magnitude 6.3 earthquake struck on Tuesday in north-eastern Japan, the second of the day to hit the area, the Meteorological Agency said.
No immediate casualties or damage were reported, and no tsunami warnings were issued.
There were no immediate reports about further damage at the stricken Fukushima Daiichi Nuclear Power Station. The plant was crippled by the March 11 magnitude 9 earthquake and ensuing tsunami.
The plant operator, the Tokyo Electric Power Co, told workers trying to stabilize the reactors there to leave.
The epicentre of the 2:07 p.m. (0507 GMT) quake was off the east coast of Fukushima prefecture at a depth of 10 kilometres, the agency said.
A magnitude 6.4 earthquake also struck eastern Japan on Tuesday morning.
