A strong earthquake with a preliminary magnitude of 6.8 jolted northeastern Japan, off Fukushima prefecture.
The Japan Meteorological Agency said no damage was reported and a tsunami advisory for the area was lifted after no waves were sighted.
Some highways were closed and high-speed bullet trains were halted after the quake, public broadcaster NHK said.
The tsunami advisory was issued for the coastal areas of Fukushima and Miyagi prefectures, which were severely damaged by the massive 11 March earthquake and tsunami.
Tokyo Electric Power Co said no abnormalities had been found at radiation monitoring posts at the crippled Fukushima Daiichi nuclear power plant, about 240km northeast of Tokyo, or the nearby Daini plant. It said cooling operations at the damaged reactors were continuing.
Tohoku Electric Power said there were no abnormalities at its Onagawa nuclear power plant, which has been shut since the March disaster.
The focus of the tremor was off the coast of Fukushima, 20km below the earth's surface, the Japan Meteorological Agency said.
The northeast coast was struck by a magnitude 9 earthquake on 11 March, the strongest on record in Japan, and a massive tsunami that triggered the world's worst nuclear crisis in 25 years at the Fukushima Daiichi plant.
The disaster left about 20,400 dead or missing.
