With communications down and access by land disrupted, rescuers were struggling to reach communities closer to the epicenter of the 7.5 magnitude earthquake that struck the small city of Palu on Friday, triggering tsunami waves as high as 20 feet.
A particular horror in several areas was liquefaction, which happens when soil shaken by an earthquake behaves like a liquid.
About 1,700 houses in one Palu neighborhood were swallowed up, with hundreds of people believed buried, the national disaster agency said.
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There was also mounting concern over Donggala, a region of 300,000 people north of Palu and close to the epicenter, and two other districts — with a combined population of about 1.4 million.
Initial reports from Red Cross rescuers who had reached the outskirts of Donggala district were chilling.
"The situation in the affected areas is nightmarish," Jan Gelfand, head of an the International Federation of Red Cross and Red Crescent Societies (IFRC) office in Jakarta said in a statement.
"The city of Palu has been devastated and first reports out of Donggala indicate that it has also been hit extremely hard by the double disaster," Gelfand said.
So far, nearly 60,000 people have been displaced and are in need of emergency help, while thousands have been streaming out of the stricken areas. Chief security minister Wiranto said on Monday the government was trying to meet survivors' immediate needs and would accept offers of international help.
"Right now, we need emergency aid," Wiranto said, referring to the foreign aid that would be airlifted to Palu, 930 miles northeast of Jakarta.
Commercial airlines have struggled to restore operations at Palu's quake-damaged airport, but military aircraft took survivors out on Monday. About 3,000 people thronged the airport hoping to get on any flight and officers struggled to keep order.
Wiranto said a navy vessel capable of taking 1,000 people at a time would also be deployed to help with the evacuation.
He said the power utility was also working to restore electricity: "Without energy, everything is crippled."