A powerful earthquake off Indonesia's Sumatra island on Thursday sent panicked people fleeing for higher ground and left eight people injured and scores of buildings damaged.

The 6.5-magnitude quake hit around dawn, waking up residents of the major port city Padang on Sumatra's west coast and sending them running from their homes.

No tsunami warning was issued after the tremor, which struck around 140 kilometres (90 miles) from Padang, according to the US Geological Survey.

In Padang two people were seriously injured by falling debris, said disaster agency spokesman Sutopo Purwo Nugroho.

He said in a nearby district six people were injured, while 54 houses and a hospital suffered mostly light damage around the region.

An 80-year-old man died of a heart attack in Padang following the quake, but it was not clear if his death was linked to the tremor, Nugroho said.

Ade Nelvi, a woman living in Padang, said she was woken by the tremor.

"It was strong and my house was shaking, so I ran to my kids' bedroom to wake them up and we ran out of the house," she said.

Electricity cut out in some places after the quake but was restored shortly afterwards, and people were not ordered to evacuate their homes.

Indonesia experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire," where tectonic plates collide.

Sumatra is particularly prone to quakes. Aceh province on the tip of the island was devastated by a quake-triggered tsunami in 2004 that killed more than 170,000 people in Indonesia and tens of thousands more in other countries around the Indian Ocean.

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