The quake produced powerful shaking along parts of Japan's eastern coast, and was felt strongly in Tokyo, but there were no immediate reports of casualties.
The prime minister's office immediately set up a crisis management office and the Tokyo Electric Power Co, or Tepco, which operates the nuclear plants, said it was checking its monitoring posts in Fukushima to ensure that there were no radiation leaks.
The Japan Meteorological Agency says a strong quake has hit off the coast of northeastern Japan, shaking Fukushima, Miyagi and other areas.
The Japan Meteorological Agency said the quake was centered about 60 kilometers (37 miles) beneath the ocean bed.
Government spokesman Katsunobu Kato said overall 950,000 homes are without power.
US imposes sanctions against Myanmar's military leaders, entities
It was adopted unanimously, although Myanmar , Russia and China envoys said they "disassociated" themselves from the resolution. Russian Ambassador Gennady Gatilov said: 'Attempts to whip up hype around the situation in Myanmar need to cease'.
He said there were several reports of minor injuries from the quake, such as a man getting hit by a falling object.
Among the hardest hit areas is the city of Soma in Fukushima, roughly 40 km north of Fukushima Daiichi nuclear plant, and the Zao ski resort in Miyagi Prefecture. He said that some trains in northeastern Japan had stopped running, and that other damage was still being checked. "And another quake", she tweeted about an aftershock.
Aerial footage broadcast by NHK showed a hillside that collapsed onto a highway in Fukushima region, severing the road.
The US Geological Survey registered the quake as magnitude 7.0 at a depth of 54 kilometres.
Earthquakes are common in Japan, which lies close to the Ring of Fire, a region around the Pacific Rim where the earth's tectonic plates meet. As many as 950,000 homes are now without power.