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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 crippled Fukushima nuclear site.

Tsunamis of up to 15 inches 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 harbors showed calm waters. The quake hit at 2:10 a.m. Tokyo time about 170 miles off Fukushima, and it was felt in Tokyo, some 300 miles 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 Dai-ichi 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 more 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.

Japan's meteorological agency issued a 3-foot tsunami advisory for a long stretch of Japan's northeastern coast, and 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.

The agency reported tsunamis of 40 centimeters in Kuji city in Iwate prefecture and Soma city in Fukushima, as well as a 20-centimeter tsunami at Ofunato city in Iwate prefecture and a 30-centimeter 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 160 miles northeast of Tokyo. About 19,000 people were killed in the disaster.

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 Tokyo Electric 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 Tokyo Electric's president to seek solutions to what he says appear to be fundamental problems.