The epicenter of the Ogasawara islands, south of Tokyo.

TOKYO - A powerful earthquake struck near remote Japanese islands and shook most of the country Saturday evening, but it occurred well beneath the earth's surface and did not trigger a tsunami warning. Several people suffered non-life-threatening injuries, and there were no reports of deaths or major damage.

The magnitude-8.5 offshore quake struck off the Ogasawara islands at a depth of 590 kilometers (370 miles), the Japan Meteorological Agency said. The US Geological Survey said the quake had a magnitude of 7.8 and a depth of 678 kilometers (421 miles).

The temblor was powerful enough to rattle most of Japan, from the southern islands of Okinawa to Hokkaido in the north. It caused buildings to sway in Tokyo - about 1,000 kilometers (620 miles) north of the Ogasawara islands - and temporarily disrupted some train services in the city. About 400 houses in Saitama prefecture, just north of the capital, were without power, according to the Tokyo Electric Power Co.

On Sunday morning, a strong magnitude-6.4 earthquake struck off of Japan's Izu islands, which are north of the Ogasawara islands, the US Geological Survey said. It struck at a depth of eight miles (13 kilometers) with its epicenter 390 miles (630 kilometers) south-southeast of Tokyo.

The earthquake was not strong enough to generate a tsunami warning or close enough to the islands to cause any significant damage or injuries, said John Bellini, a geophysicist with the USGS in Golden, Colorado. He said it is considered a separate seismic event and not an aftershock to the magnitude-8.5 quake that struck hours earlier.