Updated

A mass burial of earthquake and tsunami victims was being prepared in a hard-hit city Monday as the need for heavy equipment to dig for survivors of the disaster that struck a central Indonesian island three days ago grows desperate.

The toll of more than 800 dead is largely from the city of Palu and is expected to rise as areas cut off by the damage are reached. The magnitude 7.5 earthquake struck at dusk Friday and spawned a tsunami said to have been as high as 6 meters (20 feet) in places.

The grave being dug in Palu for 300 victims will be 10 meters by 100 meters (33 feet by 330 feet) in size 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.

Military and commercial aircraft were delivering some aid and supplies to the region. But there was a desperate need for heavy equipment to reach possible survivors buried in collapsed buildings, including an eight-story hotel in Palu where voices were heard in the rubble. A 25-year-old woman was found alive Sunday evening in the ruins of the Roa-Roa Hotel, according to the National Search and Rescue Agency, which released photos of the her lying on a stretcher covered in a blanket.

At least 832 people were confirmed dead as of Sunday evening, Indonesia's disaster agency said, with nearly all of those from Palu. The regencies of Donggala, Sigi and Parigi Moutong — with a combined population of 1.2 million — had yet to be fully assessed.

"The death toll is believed to be still increasing, since many bodies were still under the wreckage, while many have not been reached," said disaster agency spokesman Sutopo Purwo Nugroho.

The cries from beneath the Roa-Roa Hotel, which appeared to have toppled over with its walls splintered like pickup sticks, went silent by Sunday afternoon. Officials had estimated about 50 people could be inside.

"We are trying our best. Time is so important here to save people," said Muhammad Syaugi, head of the national search and rescue team. "Heavy equipment is on the way."

Metro TV showed about a dozen rescuers in orange jumpsuits climbing over debris with a stretcher carrying the body of a victim from the modest business hotel.

Other rescuers worked to free a 15-year-old girl trapped under concrete in her house in Palu after it collapsed on her family during the earthquake. Unable to move her legs under the rubble, Nurul Istikharah was trapped beside her dead mother and niece. Rescuers also tried to control water from a leaking pipe, fearing she would drown.

Istikharah was unconscious during part of the effort to free her, but rescuers kept talking to her to try to keep her awake. Others offered her food and water.

Indonesian President Joko "Jokowi" Widodo toured Palu on Sunday and said rescuers were having difficulty reaching victims because of a shortage of heavy equipment.

"There are many challenges," Jokowi said. "We have to do many things soon, but conditions do not allow us to do so."

He said authorities were deploying more heavy machinery so emergency workers can help recover more victims Monday.

The stricken areas also needed medical supplies, fuel, fresh water and experts.

It was the latest natural disaster to hit Indonesia, which is frequently struck by earthquakes, volcanic eruptions and tsunamis because of its location on the "Ring of Fire," an arc of volcanoes and fault lines in the Pacific Basin. In December 2004, a massive magnitude 9.1 earthquake off Sumatra island in western Indonesia triggered a tsunami that killed 230,000 people in a dozen countries. More recently, a powerful quake on the island of Lombok killed 505 people in August.

In Donggala, the site closest to the earthquake's epicenter, aerial footage on Metro TV showed the sugary blond sands of beaches swept out to sea, along with some buildings. Some buildings in the town were severely damaged, with plywood walls shredded and chunks of concrete scattered on the pavement. Much of the damage, however, appeared limited to the waterfront.

Palu, which has more than 380,000 people, was strewn with debris from the earthquake and tsunami. A heavily damaged mosque was half submerged and a shopping mall was reduced to a crumpled hulk. A large bridge with yellow arches had collapsed.

The city is built around a narrow bay that apparently magnified the force of the tsunami as the waves raced into the tight inlet. Nugroho, the disaster agency spokesman, said waves were reported as high as 6 meters (20 feet) in some places.

Looters hit a badly damaged shopping mall, apparently unconcerned for their safety amid ongoing aftershocks and the structure's questionable stability.

In one devastated area in Palu, residents said dozens of people could still be buried in their homes.

"The ground rose up like a spine and suddenly fell. Many people were trapped and buried under collapsed houses. I could do nothing to help," resident Nur Indah said, crying. "In the evening, some of them turned on their cellphones just to give a sign that they were there. But the lights were off later and the next day."

With hundreds injured, earthquake-damaged hospitals were overwhelmed.

Nugroho said 61 foreigners were in Palu at the time of the disaster. Most were accounted for, but one South Korean was believed to be trapped in the Roa-Roa Hotel, while three others from France and one from Malaysia were missing. The survivors were to be evacuated to the Sulawesi city of Makassar in the island's far south.

Indonesia is a vast archipelago of more than 17,000 islands that span a distance that would stretch from New York to London. It is home to 260 million people. Roads and infrastructure are poor in many areas, making access difficult in the best of conditions.

The disaster agency has said that essential aircraft can land at Palu's airport, though AirNav, which oversees aircraft navigation, said the runway was cracked and the control tower damaged.

Sulawesi has a history of religious tensions between Muslims and Christians, with violent riots erupting in the town of Poso, not far from Palu, two decades ago. Indonesia is the world's most populous Muslim country.

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Associated Press writers Margie Mason in Jakarta, Indonesia, and Stephen Wright in Makassar, Indonesia, contributed to this report.