An earthquake of magnitude 7.3 struck early Saturday off Japan's east coast, the U.S. Geological Survey said, and Japan's emergency agencies issued a tsunami advisory for the region that includes the Fukushima nuclear site.
Tsunamis of up to 40 centimetres were reported at four areas along the coast but the advisory was lifted less than two hours after the quake.
There were no immediate reports of damage on land. Japanese television images of harbours showed calm waters. The quake hit at 2:10 a.m. Tokyo time about 290 kilometres off the coast of Fukushima, and was felt in Tokyo, some 480 kilometres away.
"It was fairly big, and rattled quite a bit, but nothing fell to the floor or broke. We've had quakes of this magnitude before," Satoshi Mizuno, an official with the Fukushima prefectural government's disaster management department, told The Associated Press by phone. "Luckily, the quake's center was very far off the coast."
Mizuno said the operator of the troubled Fukushima Daiichi nuclear plant, Tokyo Electric Power Co., said no damage or abnormalities have been found so far. The plant was severely damaged in a 2011 earthquake and tsunami and has been shaken by a series of minor tremors since then.
Mizuno also confirmed that several plant workers near the coast preparing for a typhoon were ordered to evacuate to higher ground.
The Japan Meteorological Agency issued a 1-metre tsunami advisory for a long stretch of Japan's northeastern coast. It put the quake's magnitude at 7.1.
The U.S. Pacific Tsunami Warning Center did not post warnings for the rest of the Pacific.
Tsunamis of 40 centimetres were reported to have come ashore in Kuji city in Iwate prefecture and Soma city in Fukushima, as well as a 20-centimetre tsunami at Ofunato city in Iwate prefecture and a 30-centimetre tsunami at Ishinomaki in Miyagi prefecture.
All but two of Japan's 50 nuclear reactors have been offline since a March 2011 magnitude-9.0 earthquake and ensuing tsunami triggered multiple meltdowns and massive radiation leaks at the Fukushima plant, about 250 kilometres northeast of Tokyo. About 19,000 people were killed in the disaster.
Japan's meteorological agency said Saturday's earthquake was an aftershock of that quake.
A string of mishaps this year at the Fukushima plant has raised international concerns about the operator's ability to tackle the continuing crisis.
Worried Japanese regulators met with TEPCO officials this week to discuss how to prepare for a typhoon that could dump heavy rain on Fukushima on Saturday. And Nuclear Regulation Authority Chairman Shinichi Tanaka has scheduled a Monday meeting with TEPCO’s president to seek solutions to what he says appear to be fundamental problems.