TOKYO (AP) — A powerful and extremely deep earthquake struck near remote Japanese islands and shook most of the country Saturday evening, but officials said there was no threat of a tsunami, and no injuries or damage were immediately reported.

The magnitude-8.5 offshore quake struck off the Ogasawara islands at a depth of 590 kilometers (370 miles), Japan's Meteorological Agency said. The U.S. 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. Buildings swayed in Tokyo — about 1,000 kilometers (620 miles) north of the Ogasawara islands — and disrupted some train services in the city. About 400 houses in Saitama prefecture, just north of Tokyo, were without power, according to the Tokyo Electric Power Co.

At Tokyo's Roppongi Hills shopping and business complex, elevators stopped soon after the earthquake struck the area.

Yoshiyuki Sasamoto, a municipal official on Chichijima island, which is part of the Ogasawara island group, said he initially felt a mild tremor, but when he thought it was over "there was a violent shaking and I couldn't even stand on my feet."

At an inn on the Ogasawara island of Hahajima, furniture shook violently, although nothing fell or broke, innkeeper Michiko Orita told public broadcaster NHK. "It was so frightening. The entire house shook and a Buddhist altar violently swayed like I have never experienced before," she said, adding that all her guests were safe.

NHK said there were no reports of injuries or damage from the quake.

The meteorological agency did not issue a tsunami warning because the quake struck so far beneath the earth's surface. Deep offshore earthquakes usually do not cause tsunamis, and generally cause less damage than shallow ones.

In March 2011, a magnitude-9.0 earthquake rocked northeastern Japan, triggering a tsunami that killed more than 18,500 people and ravaged much of the northern Pacific coast. The depth of that quake was just 24 kilometers (15 miles), according to the meteorological agency.