JAKARTA, Indonesia - A powerful earthquake struck waters off western Indonesia late Saturday, but local officials said there was no risk of a tsunami.

The U.S. Geological Survey said the quake had a preliminary magnitude of 6.8 and hit 160 kilometres southwest of Bengkulu, a city on Sumatra island.

It was centred 26 kilometres beneath the ocean floor.

There was no risk of a tsunami, said Fauzi, an official with Indonesia's geological agency. Like many here, he only uses one name.

There were no immediate reports of damage or injuries, and residents in Bengkulu, which is frequently hit by quakes, showed few signs of panic, said Haris Said Hakim, a geological agency official based in the city.

Often powerful temblors send people fleeing their homes and running to high ground.

Indonesia is prone to seismic upheaval due to its location on the so-called Pacific "Ring of Fire," an arc of volcanoes and fault lines encircling the Pacific Basin. In December 2004, a massive earthquake off Sumatra triggered a tsunami that battered much of the Indian Ocean coastline and killed more than 230,000 people.