A magnitude 5.6 quake struck off Japan shortly after midnight at a depth of 15 (10 miles), the U.S. Geological Survey said.
It said it hit 219 km southeast of Hachijo-jima, in the Izu Islands, at 1512 GMT. It earlier gave the magnitude as 6. It was not immediately clear whether it had caused any damage.
Japan, situated on the Ring of Fire arc of volcanoes and oceanic trenches which partly encircles the Pacific Basin, accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.
(Writing by Alison Williams)