The U.S. Geological Survey says an 8.6-magnitude earthquake has struck off the northwestern coast of Indonesia, sparking fears of a tsunami throughout the Indian Ocean region.

The quake hit about 430 kilometers southwest of Banda Aceh, the provincial capital and largest city in the province of Aceh, at an estimated depth of 22 kilometers.

In 2004, a giant 9.1-magnitude quake off of Indonesia's Sumatra island triggered an Indian Ocean tsunami that killed 230,000 people, about half of them in Aceh province.

Wednesday's quake was at roughly the same depth as the 2004 Indian Ocean quake. It reportedly rattled buildings as far away as Singapore, Thailand, and India.

The Pacific Tsunami Warning Center issued a tsunami watch for 28 countries and territories bordering the Indian Ocean. It warned that earthquakes this size “have the potential to generate a widespread destructive tsunami.” But it also said it has not confirmed that a tsunami has been generated.

In Thailand, authorities are scrambling to evacuate beaches. A tsunami warning has been issued for cities along the Indonesia island of Sumatra.

If early projections do not change, the quake would be the ninth largest since 1900.

The massive quake that devastated coastal northeastern Japan last year was a magnitude 9.0 and killed around 19,000 people.