Residents of the devastated Libyan city of Derna desperately searched for missing relatives on Wednesday and rescue workers appealed for more body bags, after a catastrophic flood that killed thousands of people and swept many out to sea. Swathes of the Mediterranean city were obliterated by a torrent of water unleashed by a powerful storm that swept down a usually dry riverbed on Sunday night, bursting dams above the city. Multi-storey buildings collapsed with sleeping families inside.

A global effort to assist stricken Libya gathered pace on Thursday after catastrophic flood that killed at least 5,000 people and swept many out to sea.

Military transport aircraft from Middle Eastern and European nations, along with ships, have been ferrying emergency aid to the North African country already scarred by war.

In addition to thousands missing, tens of thousands of people have been displaced after the huge flash flood slammed into the Mediterranean coastal city of Derna on Sunday. There were fears the death toll in the city could hit 20,000.

Witnesses compared it to a tsunami after two upstream dams burst when torrential rains brought by Storm Daniel battered the region.

The wall of water ripped away buildings, vehicles and the people inside them. Many were swept out into the sea, with bodies later washing up on beaches littered with debris and car wrecks.

It was the second major disaster to hit North Africa in days, after a 6.8-magnitude earthquake killed nearly 3,000 people last Friday in Morocco.

Death tolls given by officials so far have varied, but all are in the thousands.

Hichem Abu Chkiouat, minister of civil aviation in the administration that runs eastern Libya, said more than 5,300 dead had been counted so far, and said the number was likely to increase significantly and might even double.

The “sea is constantly dumping dozens of bodies”, he said by phone.

Tariq Kharaz, a spokesperson for the eastern authorities, said 3,200 bodies had been recovered, and 1,100 of them had yet to be identified.

Derna Mayor Abdulmenam al-Ghaithi told Saudi-owned Al Arabiya television the estimated the number of deaths in the city could reach 18,000 to 20,000 based on the number of districts destroyed by the flood.

“We expect a very big number of victims,” al-Ghaithi said.

In Derna, waves rose as high as 7 metres (23 feet), Yann Fridez, head of the delegation of the International Committee of the Red Cross in Libya, told broadcaster France24.

Teacher Mohammed Derna said he, his family and neighbours rushed to the roof of their block of flats, stunned at the volume of water rushing by. It reached the second story of many buildings, he said. They watched people below, including women and children being washed away.

“They were screaming, ‘Help, help’,” he said over the phone from a field hospital in Derna. “It was like a Hollywood horror movie.”

The United Nations has pledged US$10 million to support Libya’s survivors, including at least 30,000 people it said had been left homeless in Derna. That is almost a third of the eastern Libyan city’s pre-disaster population.

Aid workers will face great challenges.

“Obstructed, destroyed and flooded roads severely undermine access to humanitarian actors,” the International Organization for Migration said, adding there were widespread power outages and communications disruptions.

“The bridges over river Derna that connect the eastern part of the city to the west have collapsed,” the IOM said.

Britain announced it was sending an “initial package” of aid worth up to £1 million (US$1.25 million). London said it was working with “trusted partners on the ground” to identify the most urgent basic needs, including shelter, healthcare and sanitation.

Abdel Fattah al-Sisi, the president of Libya’s neighbour Egypt, ordered “the establishment of shelter camps” for survivors of the Libyan disaster, according to state media.

France was sending around 40 rescuers and tonnes of health supplies along with a field hospital.

Turkey, one of the first to respond, announced Wednesday evening it was sending additional assistance by ship, including two field hospitals.

A naval vessel from Italy was also expected to be off Libya Thursday to provide logistical and medical support.

The European Union said assistance from Germany, Romania and Finland had been sent.

Algeria, Qatar and Tunisia have also pledged to help, while the United Arab Emirates sent two planes carrying 150 tonnes of aid. Another 40 tonnes of supplies took off Wednesday on a Kuwaiti flight.

Palestinian media reported a rescue mission had left from Ramallah in the occupied West Bank, and Jordan sent a military plane loaded with food parcels, tents, blankets and mattresses.

Oil-rich Libya is still recovering from the war and chaos that followed the Nato-backed uprising which toppled and killed long-time dictator Muammar Gaddafi in 2011.

The country has been left divided between two rival governments – the UN-brokered, internationally recognised administration based in Tripoli, and a separate administration in the disaster-hit east.

Agence France-Presse, Reuters, Associated Press