Massive destruction shattered the Mediterranean coastal city of Derna, home to about 100,000 people, where multi-story buildings on the river banks collapsed and houses and cars vanished in the raging waters.
Libyan emergency services reported an initial death toll of more than 2,300 in Derna alone and said over 5,000 people remained missing while about 7,000 were injured.
"The situation in Derna is shocking and very dramatic," said Osama Ali of the Tripoli-based Rescue and Emergency Service. "We need more support to save lives because there are people still under the rubble and every minute counts."
The floods were caused by torrential rains from Storm Daniel, which made landfall in Libya on Sunday after earlier lashing Greece, Bulgaria and Turkey.
Derna, 250 kilometers (150 miles) east of Benghazi, is ringed by hills and bisected by what is normally a dry riverbed in summer, but which has turned into a raging torrent of mud-brown water that also swept away several major bridges.
'The death toll is huge and might reach thousands,' warned Tamer Ramadan of the International Federation of Red Cross and Red Crescent Societies. © - / Libyan Red Crescent/AFP
The number of dead given by the Libyan emergency service roughly matched the grim estimates provided by the Red Cross and by authorities in the eastern region, who have warned the death toll may yet rise further.
"The death toll is huge and might reach thousands," said Tamer Ramadan of the International Federation of Red Cross and Red Crescent Societies, three of whose volunteers were also reported dead.
"We confirm from our independent sources of information that the number of missing people is hitting 10,000 persons so far," Ramadan told reporters via video link from neighboring Tunisia.
Elsewhere in Libya's east, aid group the Norwegian Refugee Council said "entire villages have been overwhelmed by the floods and the death toll continues to rise".
"Communities across Libya have endured years of conflict, poverty and displacement. The latest disaster will exacerbate the situation for these people. Hospitals and shelters will be overstretched."
'Catastrophic' situation
Footage on Libyan TV showed dozens of bodies, wrapped in blankets or sheets, on Derna's main square, awaiting identification and burial, and more bodies in Martouba, a village about 30 kilometers to the southeast.
More than 300 victims were buried Monday, many in mass graves -- but vastly greater numbers of people were feared lost in the waters of the river that empties into the Mediterranean.
Oil-rich Libya is still recovering from the years of war and chaos that followed the 2011 NATO-backed popular uprising which toppled and killed longtime dictator Moamer Kadhafi.
The North African country is divided between two rival governments -- the UN-brokered, internationally recognised administration based in Tripoli in the west, and a separate administration in the disaster-hit east.
Torrential rains in Libya © Sophie RAMIS, Sylvie HUSSON / AFP
Access to the eastern region is limited. Phone and online links have been largely severed, but the administration's prime minister Oussama Hamad has reported "more than 2,000 dead and thousands missing" in Derna alone.
A Derna city council official described the situation as "catastrophic" and asked for a "national and international intervention", speaking to TV channel Libya al-Ahrar.
Rescue teams from Turkey have arrived in eastern Libya, according to authorities, and the UN and several countries offered to send aid, among them Algeria, Egypt, France, Italy, Qatar, Tunisia and the United States.
'Harrowing images'
The storm also hit Benghazi and the hill district of Jabal al-Akhdar. Flooding, mudslides and other major damage were reported from the wider region, with images showing overturned cars and trucks.
Libya's National Oil Corporation, which has its main fields and terminals in eastern Libya, declared "a state of maximum alert" and suspended flights between production sites where it said activity was drastically reduced.
Flood damage in the eastern city of Derna where torrential rains caused a flashflood in a river that destroyed dams, bridges and buildings. © - / The Press Office of Libyan Prime Minister/AFP/File
Libya's UN-brokered government under Abdelhamid Dbeibah announced three days of national mourning on Monday and emphasized "the unity of all Libyans".
Aid convoys from Tripoli were heading east and Dbeibah's government announced the dispatch of two ambulance planes and a helicopter, as well as rescue teams, canine search squads and 87 doctors, and technicians to restore power.
Italy's Foreign Minister Antonio Tajani wrote that Rome was "responding immediately to requests for support" with an assessment team on its way.
The United States embassy said it had "issued an official declaration of humanitarian need in response to the devastating floods in Libya".
European Council president Charles Michel, writing on X, formerly Twitter, noted the "harrowing images from Libya" and vowed the "EU stands ready to help those affected by this calamity".
(AFP)
Neighbours said they heard screaming as people struggled to escape the flames and thick smoke © STR / AFP
State media reported that Hanoi would provide around $1,500 to families for each adult who had died © STR / AFP