A strong 6.1-magnitude earthquake struck off the northern coast of Japan's main Honshu island on Saturday, seismologists said.
No tsunami warning was issued and there were no immediate reports of damage.
The quake hit at 5.48am GMT in the Pacific about 50km from Namie town near the tsunami-ravaged Fukushima Daiichi plant, the United States Geological Survey said.
Japan's meteorological agency estimated it as 5.9 magnitude at a depth of 50km.
Fukushima operator Tokyo Electric Power Co. said there were no immediate reports of any impact on the plant, Jiji Press said.
"We have received no reports of damage so far," an official at Fukushima prefecture told AFP. Neighbouring Miyagi prefecture also had no reports of damage, a Miyagi official said.
Japan is regularly hit by powerful earthquakes and has largely adapted its infrastructure to tremors that can cause widespread damage in other, less developed countries. – Sapa-AFP