The enormous surge of storm water burst two upstream dams late Sunday and reduced the city of Derna to an apocalyptic wasteland where entire city blocks and untold numbers of people were washed into the Mediterranean.
"Within seconds the water level suddenly rose," recounted one injured survivor who said he was swept away with his mother in the late-night ordeal before they both managed to cling onto and scramble into an empty building downstream.
"The water was rising with us until we got to the fourth floor, the water was up to the second floor," the unidentified man said from his hospital bed, in testimony published by the Benghazi Medical Center.
"We could hear screams. From the window I saw cars and bodies being carried away by the water. It lasted an hour or an hour and a half — but for us, it felt like a year."
Hundreds of body bags now line Derna's mud-caked streets, awaiting mass burials, as traumatized and grieving residents search mangled buildings for missing loved ones and bulldozers clear streets of debris and mountains of sand.
In one shattered home, a rescue team pumped out the water to reveal a woman's lifeless arms still clutching her dead child, an AFP correspondent reported.
"This disaster was violent and brutal," said Yann Fridez, the head of the Libya delegation of the International Committee of the Red Cross, which had a team in Derna when the floodwaters hit.
"A wave seven meters (23 feet) high wiped out buildings and washed infrastructure into the sea. Now family members are missing, dead bodies are washing back up on shore and homes are destroyed."
'Wiped off the map'
U.N. humanitarian chief Martin Griffiths said the scale of the disaster was shocking.
"Entire neighborhoods have been wiped off the map. Whole families, taken by surprise, were swept away in the deluge of water. Thousands have died, tens of thousands are now homeless and many more remain unaccounted for."
The floods were caused by hurricane-strength Storm Daniel, compounded by the poor infrastructure in Libya, which was plunged into turmoil after a NATO-backed uprising toppled and killed longtime dictator Moamer Kadhafi in 2011.
Libya is now divided between two rival authorities — the U.N.-backed, internationally recognized government in Tripoli, and an administration based in the disaster-hit east.
U.N. World Meteorological Organization chief Petteri Taalas said many deaths could have been avoided if early warning and emergency management systems had functioned properly in the war-scarred country.
With better coordination, "they could have issued the warnings and the emergency management forces would have been able to carry out the evacuation of the people, and we could have avoided most of the human casualties," said Taalas.
He told reporters in Geneva that Libya's years-long conflict meant its meteorological "observing network has been very much destroyed, the IT systems have been destroyed."
'Climate change'
Access to Derna remains severely hampered as roads and bridges have been destroyed and power and phone lines cut to wide areas, where at least 30,000 people are now homeless.
The catastrophe's true death toll remained unknown, and officials have provided conflicting numbers.
A total of 3,840 bodies had been recovered by Wednesday, said Lt. Tarek al-Kharraz, spokesman for the interior ministry of the administration ruling eastern Libya.
But many more may have been washed out to sea or buried in the sand by the wall of muddy water that tore through the city.
The International Federation of Red Cross and Red Crescent Societies has warned that 10,000 people are missing.
Aid has been sent or promised by numerous regional nations including Algeria, Egypt, Jordan, Kuwait, Qatar, Tunisia, Turkey and the United Arab Emirates, as well as the Palestinians.
The United States has also pledged to help, and in Europe the aid effort has been joined by Britain, Finland, France, Germany, Italy and Romania.