Whole neighbourhoods in Derna were washed out to sea
The death toll from floods in Libya in one city alone stands at more than 1,500, a minister who visited the eastern port of Derna has told the BBC.
"I was shocked by what I saw, it's like a tsunami," Hisham Chkiouat, from the eastern-based government, said.
Much of Derna, which is home to about 100,000 people, is under water after two dams and four bridges collapsed.
Up to 10,000 people are recorded to be missing after the flooding as a result of Storm Daniel, the Red Crescent says.
The storm, which hit on Sunday, is also affecting the eastern cities of Benghazi, Soussa and Al-Marj.
Chkiouat, the aviation minister and part of the eastern government's emergency response committee, told BBC Newshour that the collapse of one of the dams to the south of Derna had dragged large parts of the city into the sea.
"A massive neighbourhood has been destroyed - there is a large number of victims, which is increasing each hour.
"Currently 1,500 dead. More than 2,000 missing. We don't have accurate figures but it's a calamity," he said, adding that the dam had not been maintained properly for some time.
He had told the Reuters news agency earlier that a quarter of the city had disappeared.
Tamer Ramadan, head of the International Federation of Red Cross and Red Crescent Societies (IFRC) in Libya, has told reporters the death toll is likely to be "huge".
Speaking via video link from neighbouring Tunisia, he said: "Our teams on the ground are still doing their assessment… we don't have a definite number right now. The number of missing people is hitting 10,000 persons so far."
Alongside areas in the east, the western city of Misrata was among those hit by the floods.
Libya has been in political chaos since long-serving ruler Col Muammar Gaddafi was overthrown and killed in 2011 - leaving the oil-rich nation effectively split with an interim, internationally recognised government operating from the capital, Tripoli, and another one in the east.
According to Libyan journalist Abdulkader Assad, this is hampering rescue efforts as the various authorities are not able to respond with agility to a natural disaster.
"There are no rescue teams, there are no trained rescuers in Libya. Everything over the last 12 years was about war," he told the BBC.
"There are two governments in Libya... and that is actually slowing down the help that is coming to Libya because it's a little bit confusing. You have people who are pledging help but the help is not coming."
Chkiouat said aid was on its way and the eastern administration would accept help from the government in Tripoli, which has sent a plane with 14 tonnes of medical supplies, body bags and more than 80 doctors and paramedics.
The US special envoy to Libya, Richard Norton, has said that Washington is to send aid to eastern Libya in co-ordination with UN partners and the Libyan authorities.
Egypt, Germany, Iran, Italy, Qatar and Turkey are among the countries that have said they have sent or ready to send aid.
Derna, about 250km (150 miles) east of Benghazi along the coast, is surrounded by the nearby hills of the fertile Jabal Akhdar region.
The city was once where militants from the Islamic State group built a presence in Libya, after Gaddafi's fall. They were driven out some years later by the Libyan National Army (LNA), forces loyal to Gen Khalifar Haftar who is allied to the eastern administration.
The powerful general has said eastern officials are currently assessing damage caused by the floods so roads can be reconstructed and electricity restored to help rescue efforts.
"All official bodies, especially Libya's central bank, should provide the urgent financial support needed so those executing can do their work and go ahead with reconstruction," Reuters quotes him as saying in a TV address.