The flood torrent unleashed by a powerful storm on Sunday night obliterated about a quarter of the Mediterranean city of Derna.

Whole multi-storey buildings were swept away with sleeping families inside.

The “sea is constantly dumping dozens of bodies”, Hichem Abu Chkiouat, minister of civil aviation in the administration that runs eastern Libya.

“We have counted more than 5300 dead so far, and the number is likely to increase significantly and may even double because the number of missing people is also thousands,” he said.

Tens of thousands of people had been made homeless, he said, appealing for international aid and adding that Libya did not have the experience to deal with the aftermath of such a disaster.

Officials say at least 10,000 people are feared missing or dead, although tolls of confirmed dead so far vary.

Tariq Kharaz, a spokesman for the eastern authorities, said 3200 bodies had been recovered, and 1100 of them had yet to be identified.

The United Nations migration agency, the International Organisation for Migration, said at least 30,000 people had been displaced in Derna.

The devastation was clear from high points above Derna, where the densely populated city centre, built along a seasonal riverbed, was now a wide, flat crescent of muddy water, gleaming in the sun, its buildings swept away.

At a hospital, scores of bodies wrapped in blankets were laid out on the floor in corridors or outside on the pavement, for residents to try to identify them.

Mustafa Salem said his entire family lived near the river valley opposite a mosque.

They were asleep when the flood hit, and no one has been found alive.

“We are all neighbours,” he told Reuters.

“We lost 30 people so far, 30 members of the same family.

“We haven’t found anyone.”

As Reuters was on the road to return to the city on Wednesday, aid convoys and trucks carrying bulldozers could be seen heading in.

Satellite photographs of the city from before and after the disaster showed what had been a narrow waterway through the city centre was now a wide scar, with all the buildings that had run along it gone.

Extensive damage, with buildings missing, was also clearly visible in other parts of the city.

Rescue operations are complicated by deep political fractures in the country of seven million people that has yet to rebuild a strong central government since the NATO-backed uprising that toppled Muammar Gaddafi in 2011.

An internationally recognised Government of National Unity (GNU) is based in Tripoli, in the west, while a parallel administration operates in the east, including Derna.

Libya’s Tripoli-based Prime Minister Abdulhamid al-Dbeibah called the floods an unprecedented catastrophe.

Libya’s Presidential Council head Mohammed al-Menfi has called for national unity.

The UN Office for the Co-ordination of Humanitarian Affairs said emergency response teams had been mobilised to help on the ground.

Governments including Qatar and Turkey have rushed aid to Libya.

The United Arab Emirates has sent two aid planes carrying 150 tonnes of urgent food, relief and medical supplies to eastern Libya, the UAE’s state news agency WAM reported.

-AAP