The number of deaths in Derna, Libya, could reach 20,000 following catastrophic flooding, the city's mayor has said.
Abdulmenam Al-Ghaithi told al-Arabiya TV on Wednesday that 18,000-20,000 could be dead based on the number of wiped-out districts in the city.
A spokesman for Libya's eastern administration has said more than 5,300 bodies have been recovered in Derna so far.
According to the International Organisation for Migration (IOM), at least 30,000 people have been made homeless.
Mediterranean Storm Daniel brought rain so torrential that the flooding it triggered caused two upstream dams to burst near Derna.
The city is now almost inaccessible although some aid workers have managed to reach the area.
"Bodies are everywhere, inside houses, in the streets, at sea. Wherever you go, you find dead men, women, and children," said Emad al-Falah, an aid worker from Benghazi.
Residents from the city said they heard loud explosions when the dams collapsed, sending a torrent of rushing water through Derna.
Entire residential bocks in the city have been washed away along the Wadi Derna - a main river that flows through its centre.
Of the seven roads leading to the city, only two are now accessible from its southern edge, while a number of bridges linking parts of Derna's east to its west have been destroyed.
"The city of Derna was submerged by waves seven metres high that destroyed everything in their path," Yann Fridez, head of the delegation of the International Committee for The Red Cross in Libya, told France24.
Morgues have been overwhelmed by the number of dead that have so far been recovered, with hundreds moved to nearby towns.
Derna is about 560 miles east of Libya's capital, Tripoli, and is controlled by the forces of powerful military commander Khalifa Hifter. He is allied with the east Libya government.
Aid has been sent to the affected areas by both regional governments in Libya, while Egypt, Tunisia, Algeria, Turkey, and the United Arab Emirates are among the countries to have pledged international assistance.
Joe Biden has said the United States is sending emergency funds to relief organisations and coordinating with the Libyan authorities and the United Nations (UN) to provide additional support.
On Wednesday, the King sent a message of condolence to the Chairman of the Libyan Presidential Council, Mohamed al-Menfi.
"Your Excellency," it reads.
"My wife and I are so desperately saddened by the devastating impact and loss of life caused by Storm Daniel and the subsequent floods.
"We mourn with all those who have lost their loved ones, and continue to pray for everyone whose lives and livelihoods have been affected by the horrific floods.
"I admire greatly all those who are engaged tirelessly in the rescue efforts in such dire conditions, and praise their selfless bravery.
"I know that my Government stands ready to support your needs."