JAKARTA, Indonesia (AP) — Indonesia lifted a tsunami warning issued Wednesday after a powerful earthquake off Sumatra sent islanders rushing to high ground.

The U.S. Geological Service said the earthquake had a magnitude of 7.8. It was centered under the ocean at a depth of 24 kilometers (15 miles), it said.

Shallow earthquakes are more likely to cause damage, but the USGS said the quake was located far from land, about 659 kilometers (409 miles) from the town of Muara Siberut.

Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said no damage or casualties were reported so far, but panicked people in several cities and villages on Sumatra island and in the Mentawai island chain fled to higher elevations.

Indonesia, the world's largest archipelago, is prone to seismic upheaval because of its location on the Pacific "Ring of Fire," an arc of volcanoes and fault lines circling the Pacific Basin.

A massive magnitude-9.1 quake off Indonesia in 2004 triggered a tsunami that killed 230,000 people in a dozen countries. Most of the deaths were in Indonesia's Aceh province on Sumatra.

Marjina, a resident of Sikakap in the Mentawai islands, about 690 kilometers (430 miles) from the epicenter, said the quake was felt only weakly there, but the tsunami warning caused panic among villagers.

Andi Eka Sakya, head of Indonesia's Meteorology and Geophysics Agency, said on TVOne there was only "very small" potential for a tsunami because the quake didn't occur along a major fault known as a subduction zone.

A tsunami is caused by massive displacement of seawater when a powerful earthquake lifts the ocean floor.

Australia's Bureau of Meteorology issued a marine warning for the distant Cocos and Christmas islands. It did not advise evacuations, but said strong and dangerous currents were possible and people should secure boats and avoid waterfront areas. The Joint Australian Tsunami Warning Center issued but then canceled a tsunami watch for Western Australia.

The Indian government issued a statement advising that no tsunami threat was posed for the Indian coast.