The quake occurred at 0058 GMT on Sunday, the USGS said. Its epicenter was located off the west coast of northern Sumatra in the sea 250 kilometersmiles) south southeast of Banda Aceh and 320 kilometers (200 miles) west of Medan.

The USGS, based in Golden, Colorado, early Sunday revised the magnitude of the quake from 8.5 to 8.9 on the Richter scale. It was the largest since the 1964 Prince William Sound, Alaska, earthquake which registered 9.2 and the fifth-largest since 1900.

The strongest quake on record hit Chile in 1960 and measured 9.5 on the Richter scale.

"Today's shallow, thrust-type earthquake occurred off the west coast of northern Sumatra at the interface between the India and Burma plates," the USGS said.

"In this region, the Burma plate is characterized by significant strain partitioning due to oblique convergence of the India and Australia plates to the west and the Sunda and Eurasian plates to the east.

"Preliminary locations of larger aftershocks following today's earthquake show that approximately 1,000 kilometers (620 miles) of the plate boundary slipped as a result of the earthquake," the USGS said.

In Washington, the State Department said it was closely monitoring events.

"We have no reports of US casualties at this time. It is way too early," a spokesman told AFP. "Communications are affected, so it might take more time."

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