TOKYO >> A strong earthquake struck off an island chain south of Tokyo on Tuesday, but officials said there was no danger of a tsunami.

Japan’s Meteorological Agency said the earthquake measured a preliminary magnitude of 6.9 and was very deep, about 300 miles below the ocean’s surface. Deep earthquakes generally cause less damage.

The U.S. Geological Survey put the magnitude at 6.3. Discrepancies often occur in preliminary readings because of slightly different equipment, locations and methods used in estimates, according to seismological experts.

The Japanese agency said the quake was centered west of the Ogasawara island chain in the Pacific Ocean about 600 miles south of Tokyo.

It struck at about 2:18 a.m. Hawaii time.

Some islands in the chain were shaken strongly by the quake, but it was hardly felt in Tokyo.

The area was also struck by another extremely deep earthquake on May 31, which also did not trigger a tsunami.

Japan sits along the Pacific "Ring of Fire," the arc of seismic faults around the Pacific Ocean where earthquakes and volcanoes are common.