A powerful 7.3-magnitude earthquake struck off the coast of Fukushima in northeastern Japan on Wednesday evening, triggering a tsunami advisory and plunging more than two million homes in the Tokyo area into darkness.
There were no immediate reports of casualties.
The region is part of the same area of the country that was devastated by a deadly 9.0 quake and tsunami 11 years ago that also caused nuclear plant meltdowns, spewing massive radiation that still makes some parts uninhabitable. Wednesday's quake came only days after the area marked the 11th anniversary of the disaster of March 2011.
The Pacific Tsunami Warning Center said there was no longer a tsunami threat, though the Japan Meteorological Agency kept its low risk advisory in place. NHK national television said tsunami waves of 20 centimetres already reached shore in Ishinomaki, about 390 kilometres northeast of Tokyo.
NHK footage showed broken walls of a department store building that fell to the ground and shards of windows scattered on the street near the main train station in Fukushima city, about 60 kilometres west from the coastline.
No abnormalities reported at nuclear plants
The Tokyo Electric Power Company Holdings, which operates the Fukushima Daiichi nuclear plant where the cooling systems failed after the 2011 disaster, said workers found no abnormalities at the site, which was in the process of being decommissioned.
Chief Cabinet Secretary Hirokazu Matsuno told reporters that there were also no abnormalities at two other nuclear power plants in the area.
Japan's Nuclear Regulation Authority reported that a fire alarm went off at the turbine building of No. 5 reactor at the Fukushima Daiichi but there was no actual fire. Water pumps for the spent fuel cooling pool at two of the four reactors at Fukushima Daini briefly stopped, but later resumed operation. Fukushima Daini is also set for decommissioning.
The Japan Meteorological Agency said the quake hit at 11:36 p.m. at a depth of 60 kilometres below the sea.
Japan's Air Self-Defence Force said it dispatched fighter jets from the Hyakuri base in Ibaraki prefecture, just south of Fukushima, for information gathering and damage assessment.
NHK said there were reports of fire, damage to buildings and falling rocks in Iitate town in Fukushima.
Homes lose power, trains suspended
More than 2.2 million homes were without electricity in 14 northeastern prefectures including the Tokyo region, serviced by TEPCO and another utility, Tohoku Electric Power Co., according to the companies.
Prime Minister Fumio Kishida said power was expected to be restored soon after midnight.
The quake shook large parts of eastern Japan, including Tokyo, where buildings swayed violently.
East Japan Railway Co. said most of its train services were suspended for safety checks. Some local trains later resumed service.
A Tohoku Shinkansen express train partially derailed between Fukushima and Miyagi due to the quake, but nobody was injured, Kishida said.
He told reporters that the government was assessing the extent of damage and promised to do its utmost for rescue and relief operations.
"Please first take action to save your life," Kishida tweeted.
Matsuno said there were a number of emergency calls and local authorities were scrambling to assess damage.
"We are doing our utmost in rescue operations and putting people's lives first," he said.
He urged residents in the affected areas to use extra caution for possible major aftershocks for about a week.
