Indonesia is considering declaring four villages mass graves after they were buried by landslides in last week's earthquake.

Up to 400 people are believed to have been buried alive when hillsides collapsed in the 7.6-magnitude quake and obliterated the adjacent villages in Padang Pariaman district of Sumatra island.

West Sumatra Governor Gamawan Fauzi said most of the dead would probably never be found or would be in such a state of decay that it would be better to leave them where they are.

"If after umpteen days the bodies are broken, if we dig them up probably their arms will break off, their legs will break off, it's no good," he told reporters in Padang, the provincial capital and worst-hit city.

"If the community is willing, from a religious angle it is okay not to rebury them. So that area would be designated a mass grave."

The official death toll from last Wednesday's quake stands at 704 but the Red Cross believes the final number will be more than 3,000, with hundreds of bodies still interred in the debris.