A strong 7.1-magnitude earthquake struck late Saturday off the eastern coast of Japan but no tsunami warning was issued, Japanese authorities said.
The quake produced powerful shaking along parts of Japan's eastern coast, and was felt strongly in Tokyo.
Kyodo news agency reported at least four people injured in the quake, but gave no further details. There were no immediate reports of significant damage.
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.
Saturday's quake was followed by aftershocks, including a 4.7 magnitude jolt, JMA said.
The government said around 950,000 homes lost power throughout the affected region.
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.
Prime minister Yoshihide Suga was called to his office, and broadcaster NHK said the government would set up a special liaison office to coordinate with affected regions.
Chief cabinet secretary Katsunobu Kato addressed reporters after midnight and said evaluations were under way.
"As far as damage, casualties and structural damage are being assessed," he said, adding that sections of the bullet train had been suspended due to power outages.
"Surveys are being done at Fukushima Daiichi nuclear plant," he said.
"We have received reports that Onagawa nuclear plant and Fukushima Daichi nuclear plant are not showing any abnormality," he added.
Images shown online and posted on social media showed broken glass at a shop and items spilled off the shelves at a supermarket.
Renowned author Yu Miri, who lives in Fukushima's Minamisoma city, tweeted a photo of her home, showing books, pot plants and bookcases strewn across the floor.
"My house in Odaka, Minamisoma city is all messed up," she wrote.
The US Geological Survey registered the quake as magnitude 7.0 at a depth of 54 kilometres.
Japan sits on the Pacific "Ring of Fire", an arc of intense seismic activity that stretches through Southeast Asia and across the Pacific basin.
The country is regularly hit by quakes, and has strict construction regulations intended to ensure buildings can withstand strong tremors.
In September 2018, a powerful 6.6-magnitude quake rocked Hokkaido, triggering landslides, collapsing houses and killing more than 40.