More than 800 people were confirmed dead and thousands injured in the massive earthquake and tsunami that hit the island of Sulawesi in Indonesia.

The new toll announced by the national disaster agency was almost double the previous figure.

Officials had warned last night that the death toll could rise dramatically as news arrives from remote areas of the island.

The coastline has been devastated in central Sulawesi where the 3-m high tsunami - triggered by a magnitude 7.5 earthquake on Friday - smashed into two cities and several settlements, said media reports.

There were also concerns over the whereabouts of hundreds of people who had been preparing for a beach festival when the quake struck on Friday.

The new toll announced by the national disaster agency was almost double the previous figure. Indonesian vice-president Jusuf Kalla said the final number of dead could be in the "thousands."

"It feels very tense," said 35-year-old mother Risa Kusuma, comforting her feverish baby boy at an evacuation centre in the gutted coastal city of Palu. "Every minute an ambulance brings in bodies. Clean water is scarce. The minimarkets are looted everywhere."

Indonesian Disaster Management Agency spokesman Sutopo Purwo Nugroho estimates that 2.4 million people were impacted by Friday's earthquake.

Indonesia's Metro TV on Sunday broadcast footage from a coastal community in Donggala, close to the epicentre of the quake, where some waterfront homes appeared crushed but a resident said most people fled to higher ground after the quake struck.

"When it shook really hard, we all ran up into the hills," a man identified as Iswan told Metro TV.

In Palu city on Sunday aid was trickling in, the Indonesian military had been deployed and search-and-rescue workers were doggedly combing the rubble for survivors -- looking for as many as 150 people at one upscale hotel alone.

"We managed to pull out a woman alive from the Hotel Roa-Roa last night," Muhammad Syaugi, head of the national search and rescue agency, told AFP. "We even heard people calling for help there yesterday."

The scale of casualties and damage beyond the city is still unclear, said the authorities.

Strong aftershocks have continued to hit Sulawesi leaving dozens missing. Several bodies have been lying in city streets and the injured are being treated in tents because of damage to hospitals.

After the 7.5-magnitude earthquake hit Friday, water smashed into buildings and swept away homes in the coastal city of Palu, home to 350,000 people, said witnesses to CNN.

Anxious survivors in Palu bedded down in the open air on Saturday night, heeding advice by officials not to return to their homes as a precaution. Some buildings were completely flattened.

Indonesia is prone to earthquakes because it lies on the Ring of Fire - the line of frequent quakes and volcanic eruptions that circles virtually the entire Pacific rim.

In 2004, a tsunami triggered by an earthquake off the Indonesian island of Sumatra killed 226,000 people across the Indian Ocean, including more than 120,000 in Indonesia.