Seven people were injured after a strong, 6.9-magnitude quake struck Indonesia's western Sumatra, an official said.

The epicentre of the quake, which struck at 0738 GMT, was located 43 kilometres southeast of Siberut island off western Sumatra.

It was measured at a depth of 32 kilometres.

West Sumatra provincial health crisis centre chief Jasmarizal told AFP seven people were being treated in hospital for "light injuries" in Padang city on the west coast of Sumatra.

"Five people were injured when an escalator at a mall in north Padang collapsed. Two others were hurt when the fences of their homes gave way. They had light injuries like abrasions on their arms and legs," he added.

There were no reports of casualties or damage on Siberut island, Jasmarizal said.

"But the residents there had fled to the mountains for safety," he added.

The country's geophysics agency's technical chief Suharjono said no tsunami warning had been issued.

"It was a sea quake but there's no potential of tsunami.

We'll only issue a warning if the magnitude is greater than seven," he added.