A powerful earthquake struck the waters off western Indonesia late Saturday, but it did not trigger a tsunami and there were no initial reports of injuries or damage.

The U.S. Geological Survey said the 6.8-magnitude quake hit 90 miles southwest of Bengkulu, a city on Sumatra island. It was centered about three miles beneath the ocean floor.

Though strong and shallow, the temblor did not spawn a tsunami, said Fauzi, an official with Indonesia's geological agency. Like many here, he only uses one name.

Residents in Bengkulu, a city frequently hit by quakes, showed few signs of panic, said Haris Said Hakim, a geological agency official based in the city. Powerful temblors often send people fleeing their homes and running to high ground.

The nearby town of Muko-Muko also seemed calm and did not appear to suffer any damage, said Sudirman, a military officer. He, too, uses only one name.

Indonesia is prone to seismic upheaval due to its location on the so-called Pacific "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.

A massive earthquake off Sumatra in December 2004 triggered a tsunami that killed more than 230,000 people along the Indian Ocean coastline.

Click here for more information from the U.S. Geological Survey.