An earthquake with a preliminary magnitude of 6.1 hit east of Tokyo on Wednesday but no tsunami warning was issued and there were no initial reports of damage or troubles at area nuclear plants, the Japan Meteorological Agency and local media said.
High-speed bullet trains serving northern Japan were halted and the two runways at Tokyo's Narita Airport were closed after the quake but quickly resumed operations, local media reported.
No abnormalities were reported at the Tokai No.2 nuclear power plant northeast of Tokyo, which has been shut for routine maintenance, or at Tokyo Electric Power's tsunami-hit Fukushima Daiichi and Daini plants, local media said.
The earthquake, which caused substantial shaking in Ibaraki and Chiba prefectures east of Tokyo, followed just a few hours after a magnitude 6.8 quake jolted northern Japan. A tsunami warning was issued but later lifted after that earthquake.
Just over a year ago, the northeast coast was struck by a magnitude 9 earthquake, Japan's strongest on record, and a massive tsunami, triggering the world's worst nuclear crisis in 25 years at the Fukushima Daiichi plant.
There has been a five-fold increase in the number of quakes in the Tokyo metropolitan area since the year-ago disaster, the Tokyo University Earthquake Research Institute has said.