A strong 6.0-magnitude quake struck off Indonesia's Sumatra Saturday, US seismologists said, just days after a tremor on the vast island killed dozens and left thousands homeless.

No tsunami warning was issued and there were no reports of damage after the quake struck at a shallow depth of just 23 kilometres (14 miles) off the southwest coast of the vast island, said the US Geological Survey.

US seismologists initially said it was a magnitude 6.4 quake, then revised it down to a 6.0 quake.

The epicentre was close to the remote archipelago of Mentawai. In 2010, a 7.7-magnitude quake triggered a tsunami that left more than 400 people dead on the island chain.

Suharjono, an official from the local meteorology, climatology and geophysics agency who goes by one name, said Saturday's quake was unlikely to have caused damage and there was no threat of a tsunami.

"Judging from the quake's magnitude and the distance from the epicentre to the land, I don't think the quake will have a significant impact," he said.

"There's little potential to cause damage," said the official, saying that it was felt mildly by people in two provinces on Sumatra.

The Pacific Tsunami Warning Center did not issue a tsunami alert.

It came after a 6.1-magnitude inland tremor on Tuesday struck Aceh, on Sumatra's northern tip, flattening buildings and sparking landslides in the mountainous interior of the natural disaster-prone province.

So far 35 people have been confirmed dead from Tuesday's quake and some 16,000 left homeless, according to the national disaster agency.

In 2004, a quake-triggered tsunami left more than 170,000 people dead in Aceh, as well as tens of thousands more in countries around the Indian Ocean.

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