Indonesian rescuers scrambled Monday to reach ravaged Sulawesi island as the death toll from last week’s 7.5-magnitude earthquake climbed to 844 — including 34 children at a Christian camp — and was expected to rise.

Dozens of people were believed to be trapped in the rubble of several hotels and a shopping center in the city of Palu on Sulawesi, about 930 miles from Jakarta, while hundreds more were feared buried in landslides that buried villages, Reuters reported.

Of particular concern is Donggala, a region of about 300,000 residents north of Palu that is close to the epicenter of the quake, which triggered a tsunami with waves as high as 20 feet.

Adding to the anguish was a report by a German research center that developed a warning system used by Indonesia that the tsunami alert to some residents of Sulawesi failed after the quake hit Friday.

“The problem was the communication between local authorities and people, for example on the beach, such as in Sulawesi,” Joern Lauterjung, a director at GFZ, told Reuters TV.

“If you look at the entire warning chain from the creation of a warning signal up to the last mile, as we call it, up to the local population in danger, there was a problem there,” he said.

“For example, it appears sirens did not work and there were no warnings via loudspeaker vans from police to the local population,” he added.

Widjo Kongko, a tsunami expert with the country’s technology agency, also described the patchy early warning system.

“There was no information about a tsunami recorded by the tide-monitoring station in Palu because it was not working,” he told Agence France-Presse.

The station, which tracks changes in tides, should have detected if destructive waves were headed for the city.

Indonesia’s geophysics agency did issue a tsunami warning but lifted it soon afterward. It was only later that images emerged of a surging wall of water slamming into the coast, flattening buildings and overturning vehicles.

One woman was rescued alive from ruins overnight in the Palu neighborhood of Balaroa, where about 1,700 houses were swallowed up by liquefied soil, the national rescue agency said.

“We don’t know how many victims could be buried there, it’s estimated hundreds,” said Sutopo Purwo Nugroho, a spokesman for the National Disaster Mitigation Agency.

All but 23 of the deaths were in Palu, where workers were preparing a mass grave to bury the dead as soon as they were identified.

People suffering from a lack of food also were becoming more desperate Monday.

Local media reported that about 3,000 residents had flocked to the Palu airport trying to get out. TV images showed some people screaming in anger because they were unable to board departing military aircraft.

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

Meanwhile, Indonesian President Joko “Jokowi” Widodo authorized the acceptance of aid from abroad, said disaster agency spokesman Sutopo Purwo Nugroho.

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 of Jakarta.

Nugroho said conditions in the Balaroa and Petobo sections of Palu were particularly bad because the quake caused loose soil to turn into thick, heavy mud that unleashed massive damage.

“In Petobo, it is estimated that there are still hundreds of victims buried in mud material,” Nugroho said, adding that nearly 50,000 people have been displaced from their homes in Palu alone.

The city is built around a narrow bay that magnified the force of the tsunami as the waves swept into the tight inlet.

“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 tearfully.

“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.”

Villagers expressed frustration that it took rescuers until Monday to reach Petobo.

Edi Setiawan, 32, said he and fellow villagers were able to rescue five children and four adults, including a pregnant woman — but his sister and father were not among them.

“My sister was found embracing her father,” he said. “My mother was able to survive after struggling against the mud and being rescued by villagers.”

Another villager, 52-year-old Idrus, who uses 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. Now their cries are no longer heard.”

With Post wires