Japan's Meteorological Agency issued a 1-meter (3-foot) tsunami warning for a long stretch of Japan's northeastern coast. It put the magnitude of the quake at 7.1. The U.S. Pacific Tsunami Warning Center did not post warnings for the rest of the Pacific.
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. Saturday Tokyo time (1710 GMT) about 290 kilometers (170 miles) off Fukushima. Japanese broadcaster NHK reported that Tokyo Electric Power Co., the operator of the Fukushima plant, ordered workers near the coast to move to higher ground. Japanese news service Kyodo said there were no signs of trouble at the plant.
The tremor was felt in Tokyo, some 300 miles (480 kilometers) away.
All but two of Japan's 50 reactors have been offline since the March 2011 magnitude-9.0 earthquake and ensuing tsunami triggered multiple meltdowns and massive radiation leaks at the Fukushima Dai-ichi nuclear power plant, about 250 kilometers (160 miles) northeast of Tokyo. About 19,000 people were killed.