The US Geological Survey said the undersea quake struck at 3:08 pm (0808 GMT) some 312 kilometres (194 miles) west-southwest of the North Sumatra capital Medan, at a depth of 34 kilometres.

The quake rocked the region worst hit by the Indian Ocean tsunami in December 2004, when 168,000 people were killed in Aceh, located at the northern tip of Sumatra island.

Indonesia's meteorological agency put the initial magnitude at 6.6 but later upgraded it to 7.3. It said the quake struck 42 kilometres northwest of Sinabang, the main town on Simeulue island, off the west coast of Sumatra.

Aftershocks measuring 5.5 and 5.3 hit shortly afterwards, it said.

"Three are dead, 25 seriously injured, many buildings are damaged" on Simeulue, health ministry official Rustam Pakaya said in a text message.

"People have evacuated to the mountains."

Bobby Saputra, head of the disaster mitigation centre for Aceh, told ElShinta that the three dead, aged in their 60s or 70s, were from Kampung Aie in central Simeulue. He did not say how they were killed.

The Hawaii-based Pacific Tsunami Warning Centre briefly issued a local watch bulletin, saying that a tsunami could affect coastal areas within a 100-kilometre radius of the quake's epicentre.

Thailand's disaster warning centre also issued a tsunami alert for the resort island of Phuket and five nearby provinces, warning officials along the Andaman coast to prepare for a wave, but lifted it about an hour later.

Suharjono, from Indonesia's meteorology office, told AFP that there had been no tsunami potential as the quake's epicentre was close to the coastline rather than far out at sea.

Zainul Tahar, the head of Aceh's search and rescue office, told AFP that he had earlier spoken with officials at the port authority in Sinabang and was told there was no damage there, though the quake sparked mass panic.

Yusran, a resident in Sukajaya village on Simeulue's east coast, told AFP by phone that no one had been injured there and buildings remained intact.

"But people here are very shocked as the quake was very powerful," he added.

In Aceh's capital Banda Aceh, the quake was felt for about two minutes and people initially ran outside in panic, but quickly calmed down, an AFP correspondent said.

ElShinta radio also quoted listeners as saying people had rushed out of buildings in a panic in Medan.

The Malaysian meteorological department said tremors were felt along the country's west coast and in northeastern Kelantan state. According to witnesses on the resort island of Penang, the tremors were felt for a minute.

Indonesia sits on the Pacific "Ring of Fire" where continental plates meet, causing frequent seismic and volcanic activity.

Simeulue was one of the islands closest to the 2004 quake's epicentre, but the tsunami killed fewer than 10 people there partly because the 80,000-strong population recognised the receding sea as a sign of disaster and fled inland.

In 2005, entire villages on Simeulue were destroyed by a quake which killed at least 17 people.

In Thailand, the 2004 tsunami struck six provinces on the Andaman Sea, killing some 5,400 people, about half of whom were foreign holidaymakers.

burs/sb/sst

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