Amid the horror of a magnitude 7.5 earthquake that triggered a tsunami in Indonesia, leaving more than 800 dead, came word Sunday of heroic rescue attempts in the rubble of a ravaged city.

A 25-year-old woman was pulled alive from the ruins of the Roa-Roa Hotel in Palu, a coastal community on Sulawesi Island devastated by the disaster and the focus of rescue efforts, Indonesia's National Search and Rescue Agency said.

Rescuers scrambled to free a 15-year-old girl trapped for two days next to her dead mother under concrete when her house collapsed.

Dramatic photos show a girl with dazed eyes, identified as Nurul Istikharah, reaching out to an emergency responder in an orange jumpsuit as another rescuer tries to lift her from the muddied water. Fearing the girl could drown, crews desperately tried to stop water from a nearby leaking pipe.

The rescue of the woman from the Roa-Roa was a bright spot for anguished rescuers. Some, who were awaiting heavy equipment, have been picking through the rubble by hand.

Officials said they could hear voices begging for help Saturday from the remnants of the collapsed hotel and estimated 50 people were trapped inside. By Sunday, there was only silence.

“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.”

The death toll has more than doubled to 832 from the twin disasters that struck Friday evening, crumbling buildings, sweeping away homes and flattening communities. Most of the deaths are from Palu. The regencies of Donggala, Sigi and Parigi Moutong – which have a combined population of 1.2 million – had yet to be completely assessed.

“The death toll is believed to be still increasing since many bodies were still under the wreckage, while many have not been reached,” rescue agency spokesman Sutopo Purwo Nugroho said. He said a mass burial would be held Sunday for health reasons.

More:Powerful earthquake rocks central Sulawesi in Indonesia; 1 dead

Heartbroken family members peered into yellow and blue body bags lining the streets of Palu, a city of 380,000, in a search of loved ones. The community is built around a narrow bay that may have intensified the power of the tsunami waters as they hit. Waves were reported as high as 20 feet in some places.

Residents said dozens of people could still be buried under collapsed homes.

“The ground rose up like a spine and suddenly fell,” Nur Indah said. “Many people were trapped and buried under collapsed houses. I could do nothing to help. 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.”

Aid and supplies were sent to the area via military and commercial aircraft, including helicopters. The area lacked medical supplies, fuel and fresh water.

Humanitarian aid agency World Vision was one of several groups moving to respond. The group, which has nearly 40 staff members based in Palu, was already responding to an earlier earthquake when the latest disaster unfolded.

"Ensuring that survivors have their immediate needs met with adequate shelter, food and water will be critical over the coming days," said Doseba Sinay, national director in Indonesia. "It will also be crucial to ensure children are cared for."

Indonesian President Joko “Jokowi” Widodo, who toured Palu on Sunday, said the challenges were staggering. "We have to do many things soon, but conditions do not allow us to do so,” he said.

The tragedy is 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. Last month, a powerful quake on the island of Lombok killed 505 people.

Contributing: The Associated Press