A powerful but extremely deep earthquake has struck off Japan's Ogasawara islands, but officials say there is no danger of a tsunami.

Japan's Meteorological Agency says the offshore earthquake struck Saturday at 8:24 p.m. at a depth of 590 kilometers (370 miles). The U.S. Geological Survey says the quake had a magnitude of 7.8 and a depth of 678 kilometers (421 miles).

Public broadcaster NHK said there were no immediate reports of injuries or damage.

The meteorological agency did not issue a tsunami warning because the quake struck so far beneath the earth's surface.

The Ogasawara islands are about 1,000 kilometers (620 miles) south of Tokyo.