An earthquake of magnitude 7.3 struck off Japan's east coast, near the crippled Fukushima nuclear site, the U.S. Geological Survey said.
Japan's emergency agencies declared a tsunami warning for the area of Honshu.
The National Tsunami Warning Center says there is no tsunami danger for Hawaii, Alaska, British Columbia, Washington, Oregon and California.
The quake hit at 10:10 a.m. California time, 2:10 a.m. Japan time, about 170 miles off Fukushima. Tremors were felt as far away as Tokyo, some 300 miles away.
"A destructive Pacific-wide tsunami is not expected and there is no tsunami threat to Hawaii," a Pacific Tsunami Warning Center alert stated.
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.
The 2011 quake was so powerful that it moved Japan's main island eight feet. A resulting tsunami rolled all the way across the Pacific Ocean until it reached California and heavily damaged the Santa Cruz Harbor.
Japan and the surrounding islands straddle four major tectonic plates: Pacific plate; North America plate; Eurasia plate; and Philippine Sea plate.