The U.S. Geological Survey says an 8.6-magnitude earthquake has struck off the northwestern coast of Indonesia, raising tsunami alerts in several countries around 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. An 8.2-magnitude aftershock was reported by the USGS about two hours after the initial earthquake.

Officials have issued a tsunami watch for Indonesia, India, Sri Lanka, the Maldives and the British territory of Diego Garcia. Kenya's government has also issued a tsunami alert for the country's coastal areas.

However, an expert says the earthquake's movement was horizontal rather than vertical, creating less risk of a large displacement of water needed to trigger a tsunami.

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

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

Indonesian President Susilo Bambang Yudhoyono said the situation is “under control” in Aceh and there is no immediate threat from a tsunami. No casualties have been reported so far from the quake, which sent citizens in Aceh scurrying out of buildings and into the crowded streets. Electricity was also reportedly briefly cut in some areas of the province.

Officials issued coastal evacuation orders throughout the region. Authorities scrambled to evacuate beaches and warned residents to get to higher ground.

Somchai, the general manager of the Centara Beach Resort on Karon Beach in Phuket, Thailand, told VOA that while government sirens came late, his resort was prepared.

“We directly called the guests to the room. For all of them. And we put the warning alarm so they can hear everywhere in the hotel. And now our guests, most of them, [have] come up to the meeting point,” Somchai said.

Torsak Wnichkhajorn, the former director of the Thai Meteorological Department, told VOA that the country's tsunami warning system has not detected a wave, but warned it is still possible that a tsunami could be generated.

If early projections do not change, the quake would be tied for the ninth largest since 1900. Earlier preliminary readings put the magnitude at 8.9.

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