A moderate quake with a magnitude of 5.4 has struck northeastern Japan near the zone devastated last year by the massive earthquake and tsunami that triggered a nuclear crisis.
There were no immediate reports of injuries or damage in the quake Saturday. No tsunami warning was issued.
The U.S. Geological Survey says the earthquake struck at 2:25 a.m. local time Saturday (1725 GMT) about 24 miles (40 kilometers) north of Mito, the capital of the Ibaraki Prefecture on the main island of Honshu.
The area neighbors the Fukushima Prefecture, where a quake and tsunami in March left more than 21,000 people dead or missing.