Tokyo (CNN) -- A powerful earthquake struck Japan on Thursday, triggering a tsunami warning for one prefecture and advisories in other prefectures.
The Japan Meteorological Agency said the quake was a magnitude of 7.4. The U.S. Geological Survey said it was 7.1.
There were no reports of casualties from anywhere in the earthquake zone, the National Police Agency said.
Workers evacuated the Fukushima Daiichi nuclear plant following the quake, the Tokyo Electric Power Company said. Tokyo Electric said it has communication with the plant and the power is still on there. There were no immediate reports of damage, it said.
The quake's epicenter was off the coast of Miyagi in northeastern Japan, the Japan Meteorological Agency said.
The U.S. Geological Survey said the quake was centered 41 miles (66 kilometers) from Sendai -- one of the areas worst hit by last month's 9.0-magnitude quake -- and 73 miles (118 kilometers) from Fukushima, where a crisis has been under way at the nuclear plant since last month's tsunami.
Public broadcaster NHK reported a tsunami warning for Miyagi prefecture, saying people in that area should evacuate away from the shore to a safe place.
NHK also reported tsunami advisories for the Pacific coast of Aomori Prefecture, and for the Iwate, Fukushima, and Ibaraki Prefectures.
The Pacific Tsunami Warning Center said based on all available data, "a destructive Pacific-wide tsunami is not expected and there is not a tsunami threat to Hawaii."
The quake was centered 207 miles (333 kilometers) from Tokyo, the U.S. Geological Survey said.
It was 15.9 miles (25.6 kilometers) deep, the agency reported.
It took place shortly after 11:30 p.m. local time (10:30 a.m. ET).
http://www.cnn.com/2011/WORLD/asiapcf/04/07/japan.quake/index.html?iref=NS1
TOKYO A strong aftershock rattled Japan on Thursday night, knocking out power across a large swath of the northern part of the country nearly a month after the devastating earthquake and tsunami that flattened the northeastern coast.
Japan's meteorological agency issued a tsunami warning but canceled it about 90 minutes later. Officials said power was out in all of three northern prefectures and in parts of two others.
There were no immediate reports of serious injuries or damage. The aftershock was the strongest since the March 11 megaquake and tsunami that killed some 25,000 people, tore apart hundreds of thousands of homes and caused an ongoing crisis at a nuclear power plant.
The operator of the tsunami-ravaged Fukushima Dai-ichi nuclear plant said there was no immediate sign of new problems caused by the aftershock, and Japan's nuclear safety agency says workers there retreated to a quake-resistant shelter in the complex. None were injured. The crisis there started when the tsunami knocked out cooling systems. Workers have not been able to restore them.
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Thursday's quake knocked out several power lines at the Onagawa nuclear power plant north of Sendai, which has been shut down since the tsunami. One remaining line was supplying power to the plant and radiation monitoring devices detected no abnormalities. The plant's spent fuel pools briefly lost cooling capacity but an emergency diesel generator quickly kicked in.
Officials said the aftershock hit 30 miles under the water and off the coast of Miyagi prefecture. The U.S. Geological Survey registered it as a magnitude 7.1.
Buildings as far away as Tokyo shook for about a minute.
Steve Nagato, a U.S. citizen who works as a technology consultant there, was on the subway when he felt "not much more than a very noticeable wobble."
"We were told that there had been an earthquake, and the cars stopped in the middle of the tunnel," Nagato told msnbc.com. "I looked around the see if anyone showed any concern, but basically people just pretended they didnt hear it. Conversations continued without skipping a beat."
The quake struck at 11:32 p.m. local time. Moments beforehand, residents in the western Tokyo suburb of Fuchu were warned on a neighborhood public address system of an imminent quake.
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In Ichinoseki, inland from Japan's eastern coast, buildings shook violently, knocking items from shelves and toppling furniture, but there was no heavy damage to the buildings themselves. Immediately after the quake, all power was cut. The city went dark, but cars drove around normally and people assembled in the streets despite the late hour.
Prime Minister Naoto Kan huddled with staff members in his office shortly afterward, according to deputy Cabinet spokesman Noriyuki Shikata.
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A separate government emergency response team met shortly after midnight to monitor any reports of damage and urged firefighters, police and other emergency personnel to aid those in need.
Paul Caruso, a geophysicist at USGS, said the quake struck at about the same location and depth as last month's huge one.
Another USGS geophysicist, Don Blakeman, said it was the strongest aftershock since March 11, although several aftershocks on that day were bigger.
In the search for victims from the March tsunami and quake, more than 300 police on Thursday fanned out inside the evacuation zone after officials said radiation levels there had dropped enough to allow crews back in, The New York Times reported.
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