A strong 7.3-magnitude earthquake struck off Japan's east coast late Saturday, rattling the region hit by the powerful 2011 quake, tsunami and nuclear meltdown just weeks before the disaster's 10th anniversary.
The quake produced powerful shaking along parts of Japan's eastern coast, and was felt strongly in Tokyo, but triggered no tsunami alert.
Kyodo news agency reported at least 30 people injured, but gave no further details.
There were no immediate reports of significant damage, though local news broadcast images of a landslide on a highway.
Japan's meteorological agency said the quake hit at 11:08 pm (1408 GMT) at a depth of 60 kilometres (37 miles) in the Pacific off Fukushima - near the epicentre of the 2011 killer quake which triggered a towering tsunami and killed more than 18,000 people.
The agency initially reported the strength of the quake as 7.1, but later revised the figure upwards. It said the quake was considered an aftershock of the massive 2011 temblor.
Aftershocks continued to rattle the region in the hours afterwards and officials cautioned local residents to be vigilant. A handful of people were reported to have sought shelter at evacuation centres.
"We are working quickly to collect information but we still have no details to announce. There were some unconfirmed reports about landslides but we are still checking," Mikihiro Meguro, an official from the Fukushima prefectural government, told AFP.
Around 950,000 homes lost power throughout the affected region, but no abnormalities were reported at the Fukushima nuclear plant, 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.
'All messed up'
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 posted online 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, potted plants and other belongings strewn across the floor.
"My house in Odaka, Minamisoma city is all messed up," she wrote.
"I hear the ground rumbling. 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. It was not immediately clear if anyone was hurt.
The US Geological Survey registered the quake at a revised magnitude of 7.1 with a depth of 51 kilometers.
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.