A tsunami wave hit shore in Palu, Indonesia Sulawesi Island, on Friday, when tens of thousands of people where taking part in a beach festival. Picture: AMAS/Social Media/via REUTERS ANA

A tsunami swept away buildings and killed hundreds of people on the central Indonesian island of Sulawesi, dumping victims across a devastated landscape that rescuers were struggling to reach yesterday, hindered by damaged roads and broken communications.

Disaster agency spokesperson Sutopo Purwo Nugroho said more than 384 people were known to have been killed in the hard-hit city of Palu alone.

The nearby city of Donggala and the town of Mamuju were also ravaged by the magnitude 7.5 earthquake and tsunami, but had not yet been reached by aid due to damaged roads and disrupted telecoms.

Nugroho said “tens to hundreds” of people were taking part in a beach festival in Palu when the tsunami struck at dusk on Friday. Their fate was unknown.

In some places, the water rose as high as 6m.

“We got a report over the phone saying there was a guy who climbed a tree up to 6m high,” Nugroho said.

Palu, which has more than 380000 people, was strewn with debris from collapsed buildings.

A mosque heavily damaged by the quake was half submerged and a shopping mall was reduced to a crumpled hulk.

A tsunami wave hit shore in Palu, Indonesia Sulawesi Island, on Friday, when tens of thousands of people where taking part in a beach festival. Picture: AMAS/Social Media/via REUTERS ANA

A large bridge with yellow arches collapsed. Bodies lay partially covered by tarpaulins and a man carried a dead child through the wreckage.

The city is built around a narrow bay that apparently magnified the force of the tsunami as water raced into the inlet.

Indonesian TV showed a dramatic smartphone video of a powerful wave hitting Palu, with people screaming and running in fear.

The water smashed into buildings and the damaged mosque.

Hundreds of people were injured and hospitals, damaged by the quake, were overwhelmed.

Communications was difficult because power and telecoms were cut, hampering search and rescue efforts.

“We hope there will be international satellites crossing over Indonesia that can capture images and provide them to us so we can use the images to prepare humanitarian aid,” Nugroho said.

Indonesia is a vast archipelago of more than 17000 islands that are home to 260 million people.

Roads and infrastructure are poor in many areas, making access difficult in the best of conditions.

The disaster agency said essential aircraft can land at Palu’s airport, though AirNav, which oversees aircraft navigation, said the runway was cracked and the control tower damaged.

AirNav said one of its air traffic controllers, 21, died in the quake after staying in the tower to ensure a flight he had just cleared for departure was airborne safely. It did.

More than half of the 560 inmates in a Palu prison fled after its walls collapsed during the quake, said its warden, Adhi Yan Ricoh.

Ricoh said there was no immediate plan to search for the inmates because the prison staff and police were consumed with the search and rescue effort.

Indonesian President Joko “Jokowi” Widodo said on Friday night that he instructed the security minister to co-ordinate the government’s response to the disaster.

Jokowi also told reporters in his hometown of Solo that he called on the country’s military chief to help with search and rescue efforts.

UN spokesperson Stephane Dujarric said officials were in contact with Indonesian authorities and “stood ready to provide support as required.”