Ten thousand people are missing in Libya after Storm Daniel dumped nearly eight months of rain on the north African nation, causing two dams to burst and send torrents downstream.

A quarter of the city of Derna, in the east, was wiped out by a “tsunami” that smashed buildings and may have swept thousands of people away. There are reports of bodies strewn across the ravaged landscape.

International relief agencies said 10,000 people were missing across the country, while the latest reported death toll from a government official was 5200.

“The death toll is huge,” said International Federation of Red Cross and Red Crescent Societies spokeswoman Tamer Ramadan.

At least 1000 bodies have been recovered in the ruined city of Derna (population 90,000), where morgues are full and scattered corpses are rotting.

A Libyan government minister said the water unleashed from the two dams was like a tsunami. Four bridges collapsed.

“I was shocked by what I saw, it’s like a tsunami…I cannot describe it,” said Hisham Chkiouat, from the eastern-based government.

“Bodies are lying everywhere – in the sea, in the valleys, under the buildings.

“The number of bodies recovered in Derna is more than 1000,” Mr Chkiouat said.

“I am not exaggerating when I say that 25 per cent of the city has disappeared. Many, many buildings have collapsed.”

Libya was already a country crumbling with poor infrastructure from more than a decade of conflict before Storm Daniel barrelled across the Mediterranean this week.

Footage of the damage has been described as “staggering” with overturned vehicles piled on rubble, and remnants of buildings where neighbourhoods once stood.

Videos showed a wide torrent running through Derna’s city centre after dams burst, with ruined buildings on either side.

According to Libyan experts, it was the largest natural disaster in the country since the Al-Marj earthquake in 1963.

Relief and rescue workers said that the massive damage caused by the violent storm has hampered relief efforts.

Two rival governments are vying for power in Libya, which has been plagued by unrest in recent years.

One is based in the east and the other in the capital Tripoli, in the west.

The storm system brought torrential rain to Libya on Sunday, leading to catastrophic flooding in the country’s east.

More than 300 victims were buried in mass graves, the Libyan website Babwat al-Wasat reported on Tuesday.

“Initially, those identified were buried. Due to the power outage and the lack of places to store the bodies, the other bodies were buried after photographing them, in an attempt to identify them later,” Ahmed Al-Hasadi, one of those who attended the burial ceremony, told the DPA news agency.

He added that entire families were among the victims.

The storm swept through the entire so-called Green Mountain region and its largest cities, including Derna, Al-Bayda, Al-Marj, Shahat, and Sousse, in addition to villages and towns in the region.

The mayor of Shahat municipality, Hussein Boudarwisha, told DPA that “the torrents of rain flooded approximately 20,000 square kilometres in the region”.

The spokesman for the Ambulance and Emergency Service, Osama Ali, said there is one road that still leads to the city of Derna but “passing through is difficult and dangerous due to the cracks and damages left by the storm”.

Despite the difficulties and political divisions in conflict-ridden Libya, people across the country were united in offering help to the victims.

As soon as news of the magnitude of the disaster emerged, Libyans called on each other to provide assistance.

Meanwhile, the United Arab Emirates, Turkey, Egypt, Algeria, Tunisia and the European Union have offered to send urgent relief aid and search and rescue teams to support Libyan efforts in mitigating the repercussions of the floods.

Other countries, including the US, also said they would help.

-with AAP