The toll from a severe earthquake on Indonesia's Sumatra island last week has risen to 23 dead and 88 injured, an official said on Sunday, and the area is likely to experience further significant aftershocks.

The 8.4 magnitude quake struck off the coast of western Sumatra on Wednesday evening, and has been followed by at least 40 big aftershocks and several tsunami warnings, subsequently withdrawn.

Aftershocks with a magnitude ranging from 3 to 5 are likely to be felt along Sumatra's west coast for the next two weeks, the Jakarta Post reported on Sunday, citing the head of the earthquake and tsunami division of the Meteorological and Geophysical Agency.

Rustam Pakaya, a senior health ministry official, told Reuters that as of Sunday morning, a total of 23 people had died in Bengkulu and West Sumatra provinces, the two regions closest to the quake's epicentre, while 88 people had been injured.

More than 22,000 houses in the area either collapsed or were damaged, Giri Trigondo, an official at the national disaster agency, said on Sunday.

"Quake victims in some areas need food, cooking implements, tents, medicine," he said.

Many people are still sleeping out in the open, either because their homes have been destroyed or because they are too scared to return home in case of further quakes.