Libyan officials have denied that people were told not to evacuate before flash flooding from two burst dams wiped out a swathe of the city of Derna during Storm Daniel.

Reports are emerging that military ordered people to take shelter in their homes, many of which were later swept away in “tsunami”-like torrents that smashed the city.

Reuters revealed a video by the Derna Security Directorate announcing a curfew on the night of the storm “as part of the security measures to face the expected weather conditions”.

Reuters also uncovered a Facebook post by the Water Resources minister assuring Derna residents they should not worry about the dams which “are in good condition and things are under control”.

But authorities insist the military was ordering people to evacuate but many residents did not believe the soldiers who were accused of “exaggerating” the dangers.

Meanwhile officials told CNN the flood disaster that wiped out Derna neighbourhoods had happened within a span of just 90 minutes when the dams burst.

The wall of water obliterated apartments while families were asleep on Sunday night (local time) and washed people, cars and buildings to sea.

The World Meteorological Organisation said the huge loss of life could have been avoided if Libya — a failed state for more than a decade — had a functioning weather agency in place.

“If there would have been a normally operating meteorological service, they could have issued warnings,” WMO Secretary-General Petteri Taalashe said in Geneva.

“The emergency management authorities would have been able to carry out evacuations … And we could have avoided most of the human casualties.”

Other commentators drew attention to warnings given in advance, including an academic paper published last year by a hydrologist outlining the city’s vulnerability to floods and the urgent need to maintain the dams that protected it.

The death toll reached 11,000 on Saturday (AEDT), but many more bodies remain buried on the wasted landscape.

Plea for international help

The United Nations has called for equipment to help find people still trapped in the sludge.

But international aid has not yet arrived in force, according to media on the ground.

A secondary fear is now emerging of a cholera outbreak because of the lack of clean water.

“Priority areas are shelter, food, key primary medical care because of the worry of cholera, the worry of lack of clean water,” Martin Griffiths told a UN briefing in Geneva.

He said the UN humanitarian office had sent a disaster co-ordination team of 15 people to Libya who had been redeployed from Morocco, which suffered an earthquake last week.

The World Health Organisation (WHO) and other aid groups on authorities in Libya to stop burying flood victims in mass graves after a UN report showed more than a thousand people had so far been buried in that manner since the floods.

“We urge authorities in communities touched by tragedy to not rush forward with mass burials or mass cremations,” said Dr Kazunobu Kojima.

The statement called for better-managed burials in well-demarcated and documented individual graves, saying that hasty burials can lead to long-lasting mental distress for family members as well as social and legal problems.

The bodies of victims of trauma from natural disasters “almost never” pose a health threat, it said, adding the exception was when they were in or near freshwater supplies since bodies might leak faeces.

A UN report published on Thursday said more than a thousand bodies in Derna and more than a hundred bodies in Albayda had been buried in mass graves after the floods on September 11.

“Bodies are littering the streets, washing back on shore and are buried under collapsed buildings and debris,” Bilal Sablouh, Regional Forensics Manager for Africa for the ICRC, told a Geneva briefing.

“In just two hours, one of my colleagues counted over 200 bodies on the beach near Derna.”

Sablouh warned unexploded ordnances, common in some parts of Libya, posed a risk for those involved in recovering the dead.

The ICRC sent a cargo flight to Benghazi on Friday with 5000 body bags, he said.

Mohamed al-Menfi, head of the three-member council that acts as the presidency in Libya’s internationally recognised government, said on X the council had asked the attorney general to investigate the disaster.

Those whose actions or failure to act were responsible for the failure of the dam should be held accountable, along with anyone who held up aid, he said.

-with AAP