Indonesian vice-president Jusuf Kalla said the final number of dead could be in the "thousands".
The Palu area was hit by a less powerful quake earlier on Friday, which destroyed some houses, killed one person and injured at least 10 in Donggala, authorities said. "Every minute an ambulance brings in bodies".
With communications knocked out, relief officials have not been able to get any information from Donggala regency, an area north of Palu that is closer to the epicenter of the 7.5 magnitude quake.
This morning, dozens of people were reportedly still trapped in the rubble of a hotel in Palu.
The death toll has nearly doubled as search and rescue teams comb the rubble. "We are hoping for any help".
"We need tents, medicine, canvas, nurses..." "I have my staff on the ground, but it's impossible just to rely on their strength alone to clear this".
He was working at Mutiara SIS Al-Jufrie Airport in Palu on the central Indonesian island of Sulawesi, when a 6.1 magnitude tremor hit, followed by a 7.5-magnitude quake.
Amid the levelled trees, overturned cars, concertinaed homes and flotsam tossed up to 50 metres inland, survivors and rescuers struggled to come to grips with the scale of the disaster.
Indonesian president Joko Widodo was expected to travel to the region to see the devastation for himself on Sunday.
Many did not return to their homes as night fell and slept in makeshift shelters, terrified that powerful aftershocks could topple damaged homes.
The airport's runway and air traffic control tower were damaged in the quake, authorities said. Even deliveries by sea have posed a challenge to the affected area as the tsunami severely damaged Palu's port. Homes and other buildings in the area also suffered from flooding and structural damage.
Hospitals were overwhelmed by the influx of those injured, with many people being treated in the open air. There were widespread power blackouts.
"We all panicked and ran out of the house" when the quake hit, said Anser Bachmid, a 39-year-old Palu resident.
"Those long hours on the road are going to mean hours lost getting assistance to people who need it in the next few days", she added.
"We are having difficulty deploying heavy equipment to find victims under the rubble of buildings because numerous roads leading to Palu city are damaged", he was quoted by the Kompas newspaper as saying.
Hundreds of people had gathered for a festival on Palu's beach when the water smashed onshore at dusk.
Tributes to Agung's bravery were led by Yohannes Sirait, spokesman for Air Navigation Indonesia, who said Agung's sacrifice had potentially saved the lives of hundreds of people.
"We have detected (mobile phone) signals from inside the mall, and we are trying to find a way to get to them", Basarnas official Agus Haryono told reporters at the site.
Rescuers in Indonesia were scrambling Sunday to reach trapped victims screaming for help from collapsed buildings, while looters risked entering an unstable shopping mall to grab whatever they could find after a massive natural disaster spawned a tsunami that left more than 800 dead. A large bridge with yellow arches had collapsed.
A key access road had been badly damaged and was partially blocked by landslides, the disaster agency said. There are more than 300,000 people living there.
The initial quake struck as evening prayers were about to begin in the world's biggest Muslim majority country on the holiest day of the week, when mosques are especially busy.