TOKYO A magnitude 7.1 aftershock struck northeastern Japan late Thursday night, prompting a brief tsunami warning for areas already ravaged by a March 11 earthquake and tsunami, according to the nation's meteorological agency.
The Japanese Meteorological Agency warned of tsunami heights of up to 6.6 feet in Miyagi prefecture and slightly less than 2 feet in nearby prefectures. The tsunami warning was lifted after 90 minutes.
Japanese media reported that the Onagawa nuclear plant in Miyagi lost two of three external power systems following the aftershock but still had power from one source.
No damage from Thursday's quake was detected at the Fukushima Daiichi nuclear plant crippled by last month's disaster, and Japanese television reported that workers had been evacuated without injury. In recent weeks, workers have labored to cool the reactors at the quake- and tsunami-battered Fukushima plant.
There were no reports of injuries or damage elsewhere other than scattered telephone and power outages, but people in areas covered by the tsunami warning were warned to evacuate to higher ground. Several high-speed trains in the region were also halted successfully
Last month's magnitude 9.0 quake and tsunami killed an estimated 28,000 people and left countless others homeless.
Thursday's aftershock hit at 11:32 p.m. about 200 miles north-northeast of Tokyo, causing the Japanese capital to shake for nearly a minute. Officials say the quake struck 25 miles under the water and off the coast of Miyagi.
(Ron Lin in Los Angeles contributed to this report.)