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  (Photo: Reuters/Y.T Haryono)
  Office workers evacuate and gather in front an office building in Medan after an earthquake struck Indonesia April 11, 2012. An 8.6 magnitude earthquake struck off Indonesia on Wednesday, sending residents around the region scurrying from buildings and raising fears of a huge tsunami as in 2004, but authorities said there were no reports suggesting a major threat. Indonesian President Susilo Bambang Yudhoyono said there were no immediate reports of casualties or damage in Aceh, the Indonesian province closest to the earthquake.

An 8.7-magnitude earthquake hit off the northern coast of Indonesia Wednesday, triggering a tsunami alert for the region.

The Pacific Tsunami Warning Center (PTWC) has issued an Indian Ocean wide tsunami watch placing countries in the region, including Indonesia, India, and Australia, on alert.

"Sea level readings indicate a tsunami was generated. It may have already been destructive along some coasts," the latest PTWC tsunami alert read.

"Based on the data the threat continues for all coastal areas of the Indian Ocean," the warning added.

The powerful quake hit 308 miles off the northern Indonesian city of Banda Aceh, but was also felt as far away as Singapore, Thailand, and Sri Lanka.

"The quake was felt very strongly. Electricity is down, there's traffic jams to access higher ground. Sirens and Quran recitals from mosque are everywhere," a spokesman for the Phuket Disaster Prevention and Mitigation Center told Reuters news agency.

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"The province has turned on the warning sirens and asked people all over Phuket island to move to a safe place," the official added.

Although the initial earthquake is not expected to trigger a tsunami, experts have expressed concerns over aftershocks.

"The initial earthquake may not cause a tsunami (but) there's no reason why an aftershock, which could still reach up to 8 in magnitude, cannot still cause a tsunami," oceanographer Simon Boxall told Sky News.

Indonesia was struck by a devastating tsunami in 2004 prompted by a 9.1-9.3-magnitude earthquake in the Indian Ocean. The earthquake was one of the largest earthquakes ever recorded in history.

An estimated 170,000 people lost their lives in Aceh as a result of the 2004 tsunami.