A tsunami warning has been issued by Japanese officials on Wednesday for the prefectures of Miyagi and Fukushima following a 7.3 magnitude earthquake.
The quake shook large parts of eastern Japan, including Tokyo, where buildings shook violently.
Prime Minister Fumio Kishida said the government was working to assess the extent of any damage after the tremor.
Power company TEPCO said it was assessing the impact to the equipment at the Fukushima nuclear power station, which was hit by a devastating earthquake and tsunami in 2011 that killed more than 20,000 people. The 2011 quake was of 9.0 magnitude.
A powerful magnitude 7.3 earthquake struck off the coast of Fukushima in northern Japan on Wednesday evening, triggering a tsunami advisory and plunging more than 2 million homes in the Tokyo area into darkness.
Some 2 million people in Fukushima and Miyagi were without power, TEPCO said, while in Tokyo 700,000 people were experiencing a blackout.
The Japan Meteorological Agency said the quake hit at 11:36 p.m. at a depth of 36 miles below the sea.