6.6-magnitude quake hits Indonesia's Sumatra: USGS

The quake struck around 07:30 am (0030 GMT) some 300 kilometres (186 miles) southwest of Medan, the capital of North Sumatra province, at a depth of 45 kilometres, the US Geological Survey said.

Residents in Simeulue, a small island about 150 kilometres (93 miles) off Sumatra's west coast, said violent shaking was felt for about a minute and had caused an electricity blackout.

"People were crying, grabbing their belongings and rushing out of their homes," said an AFP reporter in Sinabang, the capital of Simeulue island.

"There is no electrical power in some areas, and I can see cracks in the walls of homes around me," he said.

"Some people are returning inside their homes, but others are still outside, afraid there may be aftershocks."

Local media and Indonesia's meteorology agency said there were no immediate reports of casualties or significant damage.

The agency placed the quake in the sea off Simeulue, but did not issue a tsunami warning. It said slight shaking was also felt in the city of Banda Aceh, about 360 kilometres from Simeulue.

The Australian Bureau of Meteorology also said the Indonesian quake posed no tsunami threat to Australia.

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