Thousands of people are feared buried under mud as authorities estimate rebuilding the devastated region will cost $700m

International aid has finally started to arrive in disaster-hit Sulawesi as emergency teams cleared roads and restored power to parts of the island devastated by last week’s earthquake.

But the official death toll of 1,558 is likely to rise much higher as hopes fade of finding survivors among the thousands of people feared buried under the mud that inundated the Indonesian island after last week’s earthquake and tsunami.

Indonesia quake: bodies sent straight to graves as Palu prioritises survivors Read more

The total death toll for the Palu city districts of Petobo and Jonooge , where more than 2,400 buildings were destroyed, has still not been calculated.

“We’re not yet able to identify affected residents but based on reports we have received from the village heads in Balaroa and Petobo alone, we estimate that there may be more than 1,000 [victims unaccounted for],” said Sutopo Nugroho, spokesperson for the national disaster agency (BNPB).

“It’s still difficult, because [the victims] are buried in mud nearly three metres deep.”

Almost a week after the disaster, strong aftershocks continued to hamper rescue efforts on Friday. There have now been 422 aftershocks in the past week, including one 6.3 magnitude tremor.

The bodies of two paragliders – one Indonesian and one South Korean – were found in the ruins of the Roa Roa hotel in Palu, where screams for help had been heard over the past few days. French rescuers also said they had been unable to locate any survivors in the rubble of Palu’s Mercure hotel despite detecting a possible sign of life on Thursday.

Facebook Twitter Pinterest A member of the French organisation Pompiers de l’urgence walks out of the heavily damaged Mercure hotel in Palu. Photograph: Aaron Favila/AP

The rescuers, using sniffer dogs and scanners, had detected what they believed was a person under mounds of rubble but when they resumed the hunt early on Friday, any sign of life had disappeared.

“Yesterday we had a heart beat and sign of breathing, there were no other movements so it means it was someone who was motionless, confined,” said Philippe Besson, president of the International Emergency Firefighters. “Today we have no signal.”

Electricity was restored to some areas of Palu on Thursday and the millions pledged in international aid started to arrive into the region. Hospitals and field clinics still continued to struggle to cope with the demand for medical care, with more than 2,500 people injured people being treated. Limited commercial flights began leaving from Palu airport but not enough to meet the demand of the thousands who gathered at the airport.

Military transport aircraft from India and Singapore arrived to help in relief efforts in central Sulawesi on Thursday, with Malaysia, South Korea and the UK also sending in aircraft to help transport supplies and evacuees.

According to government calculations, the cost of damage caused by the earthquake and tsunami would reach into the hundreds of millions of dollars. “If we are to compare with what happened in Lombok, we have an estimate of more than 10 trillion rupiah [$658m],” said Sutopo.

He added that the area’s vulnerability to natural disasters would be taken into account in the rebuilding of Palu and the surrounding cities. Sutopo said: “When we reach the rehabilitation and reconstruction process, we have to guarantee that it will be better and safer, including reorganising the city layout by taking into account the possible effects of earthquakes.”