No damage or injuries were immediately reported, and Japan's meteorological agency said there was no danger of a tsunami.
The temblor hit at 12:25 p.m. local time (0325 GMT), with the epicenter near the Ogasawara Islands, about 500 miles (800 kilometers) south of the main Japanese island, the agency said. It struck at a depth of 300 miles (480 kilometers).
Japan's meteorological agency reported a magnitude of 6.9, however, the U.S. Geological Survey said the quake was 6.6. The reason for the discrepancy was not immediately clear.