The number of people known to have died in Indonesia in Friday's earthquake and tsunami has risen to 1,347, disaster response officials say.

The death toll jumped on Tuesday from a previously confirmed figure of 844.

The 7.5-magnitude quake struck just off the central island of Sulawesi, setting off a tsunami that engulfed the coastal city of Palu.

Police are guarding shops against looters as people desperately search for food, fuel and water.

Officers initially took a lenient approach to survivors seizing basic goods, deputy national police chief Ari Dono Sukmanto said, but some people have since been arrested for stealing computers and cash.

"After day two the food supply started to come in, it only needed to be distributed," he said. "We are now re-enforcing the law."

Humanitarian relief convoys entering the city are being escorted by soldiers and police.

And there are fears some survivors may still be trapped under the rubble of buildings.