TOKYO — A large earthquake shook a broad area across eastern Japan late Saturday night, with its epicenter off the coast of Fukushima, near where three nuclear reactors melted down after a quake and tsunami nearly 10 years ago.
As of Sunday morning, no deaths had been reported from the quake, Prime Minister Yoshihide Suga said. But more than 100 people were injured, according to the state broadcaster, NHK.
The quake left nearly a million households without power across the Fukushima region and forced the closure of roads and suspension of train services. While rattled residents braced for aftershocks, a landslide cut off a chunk of a main artery through Fukushima Prefecture.
Japan’s meteorological service reported the quake’s magnitude as 7.3, up from the initial assessment of 7.1, but said there was no danger of a tsunami.
Coming a little less than a month before the 10th anniversary of what is known as the Great East Japan earthquake and Fukushima nuclear disaster, the quake rattled an area that stretched from as far north as Hokkaido to the Chugoku region in western Japan.
The greater Tokyo area felt the quake for about 30 seconds starting at 11:08 p.m., but the shaking was felt most powerfully in Fukushima and Miyagi.
The quake was an unnerving reminder of the vastly more powerful 8.9-magnitude earthquake and tsunami that devastated Japan in 2011, killing more than 16,000 people. After the subsequent nuclear disaster in Fukushima, 164,000 people fled or were evacuated from around the plant.
In comments after a meeting about the quake on Sunday morning, Mr. Suga warned residents to be prepared for aftershocks and to take precautions.
“For the next week, please stay alert to the possibility of more earthquakes” of a similar size, he said, adding, “Don’t be negligent.”
Saturday’s quake struck as Tokyo and nine other large prefectures are under a state of emergency to contain the coronavirus. Residents are encouraged to work from home and avoid going out at night, while restaurants and bars are closed at 8 each night.
Japan is also preparing to host the Summer Olympics, postponed by a year from 2020. The Games are scheduled to open on July 23.
Authorities, mobilizing in response, watch nuclear plants closely.
The prime minister’s office immediately set up a crisis management office and the Tokyo Electric Power Company, or Tepco, which maintains the disabled nuclear plants, said it was checking its monitoring posts in Fukushima to ensure that there were no radiation leaks.
Shortly after midnight, the public broadcaster NHK reported that Tepco had detected “no major abnormalities” at any of the Dai-ichi reactors where the meltdowns occurred in 2011 or at the Dai-ni plant a few miles away in Fukushima.
Early Sunday morning, Tepco said it had found that water in some of the pools that store spent nuclear fuel rods had splashed onto the pool decks inside the reactors at both the Dai-ichi and Dai-ni plants. But Tepco said no water had leaked outside the reactors.
Tepco also reported that there had been some small leaks from a tank filled with contaminated water stored on the Dai-ichi site but that the leak had been contained within a small area.
The Kashiwazaki-Kariwa nuclear plant on the west coast had suffered no damage, NHK reported.
According to Katsunobu Kato, chief cabinet secretary to Prime Minister Yoshihide Suga, about 950,000 households were left without power across the affected areas. He said that two thermal power plants in Fukushima Prefecture had been taken offline. Several bullet train lines were suspended. People in dozens of households were evacuated to shelters in several cities in Fukushima.
In brief comments to reporters just before 2 a.m., Mr. Suga advised residents not to go outside and to brace for aftershocks.
Aftershocks: What the hours and days ahead may hold.
Speaking on NHK, Takashi Furumura, a professor at the Earthquake Research Institute at the University of Tokyo, warned that a quake of this size could be followed within two or three days by another of similar scale.
The Japan Meteorological Agency said the quake’s epicenter was about 60 kilometers — or about 37 miles — off the coast of Fukushima and about 34 miles deep. On land, the strongest magnitude felt was 6-plus.
Speaking at a news conference, Noriko Kamaya, an official for the meteorological agency, said residents should be prepared for aftershocks as strong as magnitude 6 in the coming days. She described Saturday night’s earthquake as itself an aftershock of the 2011 quake.
In Minami Soma, one of the Fukushima villages evacuated after the nuclear disaster in 2011, NHK reported that severe shaking lasted for about 30 seconds on Saturday.
Yu Miri, the author of “Tokyo Ueno Station,” winner of the National Book Award for translated literature, posted photos on Twitter showing bookshelves in her nearby home downed and the floors strewn with books.
Kyodo News reported that 50 people had been injured in the Fukushima and Miyagi regions, both on Japan’s east coast.
Japan has endured a history of devastating earthquakes.
Roughly a dozen powerful earthquakes have struck Japan in the past decade, several of them triggering tsunamis and landslides that have shaken parts of the country and destroyed countless buildings.
In 2016, more than 40 people died after two earthquakes rocked the southern island of Kyushu. The largest of the two registered a magnitude of 7.0, close to the intensity of the quake felt on Saturday, and several died in fires and landslides in the mountainous region.
In 2018, dozens died and millions lost power in their homes after a powerful quake in the northern island of Hokkaido triggered landslides. The quake that summer came just days after the largest typhoon recorded in 25 years struck Japan.
Makiko Inoue, Hisako Ueno, Hikari Hida and Elian Peltier contributed reporting.