An earthquake registering magnitude 6 struck early Thursday in Japan's Fukushima province, DPA reported.
There were no immediate reports of damage from the 4:24 am quake, which had an epicentre 30 kilometres under the seafloor off Fukushima. Authorities said there was no tsunami danger.
Fukushima was struck on March 11 by a magnitude-9 quake, which caused major damage across the region and set off a tsunami that devastated coastal communities. The twin disasters damaged a powerplant, leading to a nuclear meltdown.
Tokyo Electric Power Company, operator of the Fukushima Daiichi nuclear plant, reported no immediate problems Thursday at the crippled facility, broadcaster NHK said.
The latest quake was strong enough to set skyscrapers swaying in Tokyo, 260 kilometres away.