The epicenter of the quake -- which struck at 2:06 am (1706 GMT Thursday) -- was located 13 kilometers (eight miles) north of the city of Kunisaki-shi, USGS said.
The quake struck at a depth of 82 kilometers. There was no immediate warning message issued by the Pacific Tsunami Warning Center.
More than 18,000 people died when a 9.0-magnitude undersea earthquake sent a towering tsunami barreling into Japan's northeast coast in March 2011 in the country's worst post-World War II disaster.
Cooling systems at the Fukushima nuclear plant were knocked out, sending reactors into meltdown and forcing tens of thousands of people to flee. (AFP)