Brightly colored body bags were placed side-by-side in a freshly dug mass grave on Monday, as a hard-hit Indonesian city began burying its dead from the devastating earthquake and tsunami that killed more than 840 people and left thousands homeless.

The death toll, largely from the city of Palu, is expected to keep rising as areas cut off by the damage are reached. The magnitude 7.5 earthquake struck at dusk on Friday and generated a tsunami said to have been as high as 6m in places.

Local army commander Tiopan Aritonang said 545 bodies would be brought to the grave from one hospital alone. The trench dug in Palu was 10m by 100m and can be enlarged if needed, said Willem Rampangilei, chief of Indonesia's National Disaster Mitigation Agency.

"This must be done as soon as possible for health and religious reasons," he said. Indonesia is majority Muslim, and religious custom calls for burials soon after death, typically within one day.

Local military spokesperson Mohammad Thorir said the area adjacent to a public cemetery can hold 1 000 bodies. All of the victims, coming from local hospitals, have been photographed to help families locate where their relatives were buried. Video footage showed residents walking from body bag to body bag, opening the tops to check if they could identify faces.

Around midday, teams of workers, their mouths covered by masks, carried 18 bodies and laid them in the trench. A backhoe waited to push soil on top of the dead. More burials were expected to follow.

Military and commercial aircraft were delivering some aid and supplies. But there was a need for heavy equipment to reach possible survivors buried in collapsed buildings, including an eight-story hotel in Palu where voices had been heard in the rubble.

People suffering from a lack of food and supplies were also becoming more desperate. Local television said around 3 000 residents had flocked to the Palu airport trying to get out. Footage showed some people screaming in anger because they were not able to board departing military aircraft. The airport has resumed only some commercial flights.

"We have not eaten for three days!" one woman yelled. "We just want to be safe!"

Indonesian President Joko "Jokowi" Widodo authorised the acceptance of international help, said disaster agency spokesperson Sutopo Purwo Nugroho, adding that generators, heavy equipment and tents were among the items needed. He said the European Union and 10 countries have offered assistance, including the United States, Australia and China.

"We will send food today, as much as possible with several aircraft," Widodo told reporters in the capital, Jakarta, adding that a supply of fuel was also set to arrive.