For two days, Edi Setiawan helped pull the dead and the living out of a sea of mud and debris, all of them victims of one of Indonesia's deadliest earthquakes in years.

And then, half-buried in the brown sludge, he saw two motionless bodies that broke his heart.

"I could see my father still embracing my sister," Setiawan said Monday, recounting the devastating moment he found the pair entombed in mud near their home in the city of Palu.

"I just cried," he said. "I was able to save other people, but I was unable to save my own family."

Friday's magnitude 7.5 quake killed more than 840 people and destroyed thousands of homes, triggering a humanitarian crisis with survivors now in desperate need of food, water and fuel.

Most of the casualties were caused by the quake itself and a deadly tsunami that slammed into the coastline around Palu. But hundreds of others were buried alive by a phenomenon called liquefaction, in which loose soil shaken by a quake gives way and collapses.

Disaster agency spokesman Sutopo Purwo Nugroho said Palu's Petobo neighborhood, where Setiawan lived, was especially hard-hit. "There are still hundreds of victims buried in mud" in the area, he said.

On Monday, newly arrived rescue teams were confronting the behemoth task of trying to dig them out.

Palu, a city of 380,000 on the western coast of central Indonesia's Sulawesi island, stood in ruins. Toppled cellphone towers have cut off communications, while downed power lines leave the city in darkness after the sun sets.

While thousands of desperate people swarmed the airport tarmac trying to escape on board a military aircraft that arrived with aid, burials began in a freshly dug mass grave.

When the massive quake struck on Friday, Setiawan said he was cleaning debris from another strong tremor that had cracked the walls of his home just hours earlier but left it standing.

As the 32-year-old rushed outside, "the ground I stepped on cracked ... water and mud came out, more and more from all directions."

His neighborhood seemed to be sinking.

His wife and year-old daughter were fine, but other family members, friends and neighbors were missing.

He tried to reach his parents' home, about 300 meters (yards) away, but the sea of mud that engulfed the area made it too hard to reach. With other villagers, he turned to saving whoever he could.

"I took a 2-year-old (child) on my head, a 3-year-old on my back, and held a 5-year-old while struggling to swim out from mud to the asphalt road," Setiawan said.

Villagers hurled ropes to people stuck in pools of thick mud that seemed like quicksand, and pulled them out by hand. Some of them saved his mother.

By Saturday, they had rescued 11 adults, including a pregnant woman, and two other children - although one later died.

Then they turned to the dead, recovering four bodies. It was Saturday when Setiawan saw the bodies of his father and sister in the sludge, locked in the embrace that had marked the last moment of their lives.

Many complained bitterly at the failure of rescue teams, overwhelmed by the scale of the crisis, to make it to their neighborhood in time.

Idrus, 52, who like many Indonesians uses only one name, said that "up to Saturday, we still saw many people screaming for help from the roofs."

"But we could not do (anything) to help them," he said. "Now, their cries are no longer heard."

Setiawan said the first government rescue teams arrived in his area Sunday, but because the mud was still unstable, they were only able to take photos documenting the tragic scene.

On Monday, they returned, and recovered eight bodies. n

Pitman reported from Jakarta.

Plight of Palu

The 7.5-magnitude earthquake hit around 6pm, and was followed by tsunami waves of up to 6m high. Thousands of homes and buildings have been destroyed, including an entire housing estate home to 900 people.

Officials have warned that the final death toll could rise into the thousands, with some of the worst hit areas still yet to be accessed by rescuers. As the tsunami approached land, it was travelling at up to 250mph (400km/h), with a reported wave height of up to 6 metres.

The earthquake was not expected to result in a tsunami of this scale, with the huge waves taking scientists by surprise. The full picture of what caused the size of the waves is not yet known, but there is speculation that landslides under the sea and the geography of the bay may have been contributing factors.

Palu, home to 350,000, was flattened by the tsunami, with thousands of homes, hotels and shopping malls collapsing. As the death toll continues to mount, residents also face food and fuel shortages, alongside widespread power outages.

Search efforts are largely being done by hand, as the heavy equipment required to move the rubble has not yet reached affected areas.