Update 11:30 a.m. The tsunami warning for Japan has been lifted.
Tsunami warning in effect for the same northeast coast area so badly hit by a previous tsunami a few weeks ago. A one-meter (3 foot) wave is expected, and coastal residents have been advised to evacuate to higher ground.
No alert for Hawaii or West Coast of U.S.
Live coverage from NHK World English in Japan, which reports that two of three power lines at the damaged Fukushima Daiichi nuclear power plant have gone down, and that workers have taken shelter due to the tsunami alert. No increased radiation has been reported thus far. A blackout in Sendai has also been reported.
Japan was rattled by a strong aftershock and tsunami warning Thursday night nearly a month after a devastating earthquake and tsunami flattened the northeastern coast.
The Japan meteorological agency issued a tsunami warning for a wave of up to 6 feet (two meters). The warning was issued for a coastal area already torn apart by last month's tsunami, which is believed to have killed some 25,000 people and has sparked an ongoing crisis at a nuclear power plant.
Officials say Thursday's aftershock was a 7.4-magnitude and hit 25 miles (40 kilometers) under the water and off the coast of Miyagi prefecture. The quake that preceded last month's tsunami was a 9.0-magnitude.
Buildings as far away as Tokyo shook for about a minute.
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.
U.S. Geological Survey gave the preliminary magnitude as 7.4 and it struck off the eastern coast 60 miles (100 kilometers) from Sendai and 90 miles (140 kilometers) from Fukushima. It was about 215 miles (345 kilometers) from Tokyo.
The depth was 25 miles (40 kilometers). Shallower quakes tend to be more destructive.
Hundreds of aftershocks have shaken the northeast region devastated by the March 11 earthquake, but few have been stronger than 7.0.
A Pacific Tsunami Warning Center evaluation of the quake said an oceanwide tsunami was not expected.
And from the Pacific Tsunami Warning Center
NO DESTRUCTIVE WIDESPREAD TSUNAMI THREAT EXISTS BASED ON
HISTORICAL EARTHQUAKE AND TSUNAMI DATA.
HOWEVER - EARTHQUAKES OF THIS SIZE SOMETIMES GENERATE LOCAL TSUNAMIS THAT CAN BE DESTRUCTIVE ALONG COASTS LOCATED WITHIN
A HUNDRED KILOMETERS OF THE EARTHQUAKE EPICENTER. AUTHORITIES IN THE REGION OF THE EPICENTER SHOULD BE AWARE OF THIS POSSIBILITY AND TAKE APPROPRIATE ACTION. THIS WILL BE THE ONLY BULLETIN ISSUED FOR THIS EVENT UNLESS ADDITIONAL INFORMATION BECOMES AVAILABLE.
THE JAPAN METEOROLOGICAL AGENCY MAY ALSO ISSUE TSUNAMI MESSAGES
FOR THIS EVENT TO COUNTRIES IN THE NORTHWEST PACIFIC AND SOUTH
CHINA SEA REGION. IN CASE OF CONFLICTING INFORMATION... THE
MORE CONSERVATIVE INFORMATION SHOULD BE USED FOR SAFETY. THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE PRODUCTS
FOR ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON...CALIFORNIA.