The International Federation of Red Cross and Red Crescent Societies on Monday increased its global fund appeal to 22 million Swiss francs ($22.37 million) to help 160,000 displaced people in Indonesia for 20 months.
The IFRC appeal comes after a series of earthquakes and a tsunami struck Sulawesi island on Friday and killed 844 people and displaced thousands, according to initial data.
"The situation in the affected areas is nightmarish. The city of Palu has been devastated and the first reports out of Donggala indicate that it has also been hit extremely hard by the double disaster," said Jan Gelfand, Head of IFRC Country Cluster Support office in Jakarta.
Palu, the capital of the province of Central Sulawesi, has a population of around 350,000, while the neighboring district of Donggala has some 277,000.
"Red Cross and other teams are working round the clock but the biggest challenge at the moment is getting access to all communities, and then bringing large quantities of vital relief supplies into the disaster zone. Transport links, power and communications are still down," Gelfand added.
More than 175 volunteers and staff from the Indonesian Red Cross are currently engaged in search and rescue operations in the affected areas.
The catastrophe began on Friday with a 6.1-magnitude earthquake that killed one person and left 20 wounded, which was followed by another quake of magnitude-7.5 and then a tsunami.
Hundreds of aftershocks have been registered since then while the death toll has gone up to 844 with 90 missing, 632 injured and 48,025 displaced people put up in 103 relief shelters.
Indonesia sits on the so-called Ring of Fire of the Pacific, an area of great seismic and volcanic activity that experiences about 7,000, mostly moderate, earthquakes every year.