"The Indonesian Red Cross is racing to help survivors but we don't know what they'll find there".
Authorities have been having difficulties coordinating rescue efforts as the quake caused a power outage that cut communications around Palu and the nearby town of Donggala, the closest epicentre of the tremor. Indonesian vice-president Jusuf Kalla said the final number of dead could be in the "thousands".
Many bodies were found on Saturday along the shoreline of the Indonesian city of Palu on Sulawesi island which was hit by a major natural disaster and tsunami, as the death toll rose to 48 people and hundreds unaccounted for, authorities said, Reuters reported.
Donggala's waterfront and port was extensively damaged, with houses swept into the sea and bodies trapped in the rubble, according to a Metro TV reporter on the scene.
"We have heard nothing from Donggala and this is extremely worrying", Gelfand said. "There are more than 300,000 people living there", Red Cross said in a statement.
The 7.5 magnitude quake triggered a 10-foot high tsunami which smashed into the city of Palu.
Indonesia's meteorological and geophysics agency BMKG issued a tsunami warning after the quake, but lifted it 34 minutes later.
The agency was widely criticised on Saturday for withdrawing the warning too quickly, though officials said they estimated the waves had come within the time the warning was in force.
Hundreds of people were preparing for a beach festival to celebrate Palu's anniversary.
She said communication was hard and the aid organisation had been struggling to get a proper ground assessment. Reuters was not able to authenticate the footage.
The Indonesian National Board for Disaster Management put the official death toll at 384 as of last night, all of them in the tsunami-struck city of Palu, but added that the toll was likely to rise.
Dramatic video footage captured from the top floor of a parking ramp as the tsunami rolled in showed waves bringing down several buildings and inundating a large mosque. "Electricity is out all over Palu", he said.
"I just ran when I saw the waves hitting homes on the coastline", said Palu resident Rusidanto, who like many Indonesians goes by one name.
Dozens of injured people were being treated in makeshift medical tents set up outdoors.
Photos confirmed by authorities showed bodies lined up along the street on Saturday, some in bags and some with their faces covered with clothes.
Indonesian president Joko Widodo has arrived in the region Sunday afternoon to see the devastation for himself.
On Friday night, Indonesia's president said he had instructed the security minister to coordinate the government's response to the natural disaster and tsunami.
"If he needs our help, he'll have it", Mr Morrison told the ABC on Sunday, describing the rising death toll as "horrific".
More than half of the 560 inmates in Palu's prison escaped after its walls collapsed during the quake, according to state news agency Antara, while more than 100 inmates escaped from a prison in Donggala.
Chief security minister Wiranto told TVOne the military had started sending in cargo planes from the capital Jakarta carrying relief aid.
Palu's airport was damaged in the quake, but was reopened for limited commercial flights on Sunday, authorities said.
Among the dead was a young Indonesian air traffic controller who stayed at his post when the natural disaster hit to ensure that a plane carrying hundreds of passengers took off safely.