Japan's meteorological agency said the quake hit at 11.08pm (1408GMT) at a depth of 60 kilometres (37 miles) in the Pacific, off Fukushima - near the epicentre of a 2011 killer quake which triggered a towering tsunami and killed more than 18,000.
The exact magnitude, epicenter, and depth of the quake might be revised within the next few hours or minutes as seismologists review data and refine their calculations, or as other agencies issue their report.
Government spokesman Katsunobu Kato said overall 950,000 homes are without power.
Prime Minister Yoshihide Suga headed into his office immediately after reports of the quake, and a crisis centre was set up there.
The Japan Meteorological Agency said the quake had a magnitude of 7.3, raising it from a preliminary magnitude of 7.1. It said the quake was considered an aftershock of the massive 2011 temblor.
Fukushima nuclear plant operator TEPCO said in a tweet it was checking on the status of the facility, which melted down in the wake of the 2011 tsunami. Items fell off shelves because of the shaking, NHK said.
The deadly wall of water slammed through the walls of the Fukushima Daiichi Nuclear Power Plant, knocking out the power supply and causing three nuclear reactors to melt, spewing radioactive particles into the air. 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.
There have been no reported casualties, officials said, but nearly one million homes in the region are without power. He said there were no reports of major injuries. Experts are warning of aftershocks over the next several days, including possibly larger quakes.
Some people were taking shelter at evacuation centers, and were being warned to practice social distancing because of the coronavirus pandemic.