A powerful earthquake, a magnitude of 7.2 earthquake struck the Tohoku region north of Tokyo at 11:46 a.m., the U.S. Geological Survey said on its Web site. As many as 80 people were injured when a roof in Sendai city collapsed, NHK Television reported.
The quake, also felt in Tokyo, originated in the Pacific off the coast of the prefecture, the agency said. The focus was about 20 kilometers below ground. Shinkansen bullet train services from Tokyo have been suspended temporarily. The town of Kawasaki in southern Miyagi Prefecture registered a lower 6 on the Japanese seismic intensity scale of 7, the meteorological agency said. The quake registered 4 on the scale in central Tokyo, Kyodo News informs.
One person was seriously injured and others were hurt when the roof of an indoor swimming pool in Sendai collapsed, NHK Television reported, citing local authorities. The government set up an emergency task force in Prime Minister Junichiro Koizumi's official residence in Tokyo to coordinate its response, it said in a statement.
Nippon Oil Corp., Japan's biggest petroleum refiner, said operations at its Sendai refinery were stopped after the quake. The refinery processes up to 145,000 barrels a day of crude oil. Tohoku Electric Power Co., the country's fourth-biggest generator, said the three nuclear reactors at its Onagawa plant automatically shut down, Bloomberg reports.
There were no immediate reports of damage, Tohoku Electric Power Co. spokesman Nobuyoshi Kuroda said when contacted by telephone.
A tsunami warning was issued for a 50 centimeter wave (20 inches) to reach the coast by noon local time, NHK reported, citing Japan's Meteorological Agency.
Japan, one of the world's most earthquake-prone countries, is located in a zone where the Eurasian, Pacific, Philippine and North American tectonic plates meet and occasionally shift, causing quakes. Quakes of magnitude 5 and more can cause considerable damage depending on their depth.