A powerful magnitude 7.3 earthquake rocked Japan's northeast coast off Fukushima, leaving one dead and 69 injured and reviving memories of a quake and tsunami that crippled the same region just over a decade earlier.
There were some reports of fire, the government said, and a number of people sustained injuries, but none of those immediately appeared serious. Public broadcaster NHK said one person had died.
The quake was felt in Tokyo, some 275km (170 miles) away, where the shaking of buildings was long and pronounced.
Hundreds of thousands of homes in the capital were plunged into darkness for an hour or more, although power was fully restored by the early hours of the morning local time.
Just before midnight, the quake hit off the coast of Fukushima prefecture at a depth of 60km, the Japan Meteorological Agency said.
It sparked memories of a devastating earthquake and tsunami in March 2011, a week after that disaster's 11th anniversary.
There were no abnormalities at nuclear power plants, Prime Minister Fumio Kishida told reporters. The 2011 disaster triggered a meltdown at the Daiichi nuclear plant in Fukushima that Japan is still coming to grips with.
Authorities earlier said a fire alarm had been triggered at a turbine building at the crippled plant.
Separately, a Shinkansen bullet train derailed with some 100 people on board, although there were no reports of injuries.
Utility Tokyo Electric Power Company 9501.T said that initially around 2 million households lost power on Wednesday, including 700,000 in the capital.
In northeast Japan nearly 100,000 households are still without power, according to Tohoku Electric, the local utility.
Authorities issued a tsunami warning for the region of as high as 1 metre, with waves of 20cm reported in some places. Residents in at least one coastal area were told to evacuate.
Authorities warned residents in Fukushima, Miyagi and Yamagata prefectures to expect aftershocks.
Sitting on the boundary of several tectonic plates, Japan experiences around a fifth of the world's earthquakes of magnitude 6 or greater.
