A 6.5-magnitude earthquake hit off the Indonesian island of Sumatra early Thursday, US seismologists said, sending panicked people running from their homes but not causing any casualties or damage.

Many people were woken by the quake around dawn and fled their homes in Padang, about 140 kilometres (90 miles) from the epicentre, an AFP journalist in the city said.

The quake happened at 5:56 am local time (2256 GMT Wednesday), and struck at a depth of 50 kilometres, according to the US Geological Survey. No tsunami warning was issued.

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, said the AFP journalist, and people were not ordered to evacuate their homes.

Wandono, a senior official from Indonesia's Meteorology, Climatology and Geophysics Agency, said the quake did not have the potential to cause a tsunami.

"So far we have not received any reports of damage," added the official, who like many Indonesians goes by one name.

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

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