At least 30,000 people have been displaced in the town hardest hit by floods in Libya.
Meanwhile, a minister has said 5,300 bodies in the country’s east have been recovered – with the number of fatalities expected to rise significantly.
Officials are appealing for international help, and have warned Libya doesn’t have the necessary experience to deal with a disaster of this scale.
Storm Daniel caused significant damage to roads and telecoms networks on Sunday – with strong winds and sudden heavy rainfall devastating the town of Derna.
The town is about 560 miles (900km) east of the capital, Tripoli.
The “sea is constantly dumping dozens of bodies”, Hichem Abu Chkiouat, minister of civil aviation in the administration that runs eastern Libya, said, adding that reconstruction would cost billions of dollars.
As Storm Daniel pounded the coast on Sunday night, Derna residents said they heard loud explosions when dams outside the city collapsed.
Floodwaters washed down the river Wadi Derna, which runs from the mountains through the city and into the sea.
Waves measuring seven meters (23ft) high “destroyed everything in their path,” Yann Fridez, head of the delegation of the International Committee for The Red Cross in Libya, told France24.
“The human toll is enormous.”
Rescue teams are still trying to recover bodies scattered in the streets and under rubble in the city.
Ahmed Abdalla, a survivor who joined the search and rescue effort, said they were putting bodies in the garden of a local hospital before taking them for burial in mass graves at the city’s only intact cemetery.
Libya’s neighbours, Egypt, Algeria and Tunisia, as well as Turkey and the United Arab Emirates, have sent rescue teams and humanitarian aid.
President Joe Biden also said the United States is sending emergency funds to relief organisations and coordinating with the Libyan authorities and the UN to provide additional support.
But the arrival of aid has been hampered due to the destruction of roads leading to the city. Bridges over the river Derna that link the city’s eastern and western parts have also collapsed, according to the UN’s migration agency.