Thousands of people have been killed in Libya in the flooding caused by heavy rains that devastated parts of the country this weekend, a disaster exacerbated by the collapse of two dams in the coastal city of Derna, aid agencies said on Tuesday.

Tamer Ramadan, head of the Libya delegation for the International Federation of Red Cross and Red Crescent Societies, said the death toll from the flooding was expected to reach thousands in coming days. Speaking to reporters at a U.N. briefing via videoconference from Tunisia, he said 10,000 people were missing, and that those figures were based on reports from the Libyan Red Crescent on the ground.

A Libyan ambulance and emergency services department said least 2,300 people had died and more than 5,000 were missing after heavy rainfall over the weekend in the northeast of Libya swelled waters over riverbanks, sweeping away homes and cutting off roads.

The collapse of the dams, south of Derna, deepened the disaster after they unleashed water that swept through the city and carried “entire neighborhoods” into the sea, Ahmed al-Mismari, a spokesman for the Libyan National Army, the dominant political force in the area, said in a televised news conference on Monday.

Libya has been divided for years between an internationally recognized government based in Tripoli and a separately administered region in the east, including Derna. The ambulance and emergency services department that provided the numbers of dead and missing is affiliated with the government in the west, which said it had sent rescue teams to the east.

An official in the administration that controls the east told Reuters on Tuesday that more than 1,000 bodies had been recovered so far.

Mr. al-Mismari said in the televised news conference on Monday that more than 2,000 people were believed to be dead in Derna alone, and that as many as 5,000 to 6,000 were missing, a number that he said “could increase massively,” with conditions making it difficult to orchestrate rescue and aid operations.

“It’s the first time we’ve been exposed to this type of weather conditions,” Mr. al-Mismari said. Citizens who escaped from Derna left the city “as if they were born today, with nothing,” he said.

It was unclear on Tuesday how the different authorities in Libya were coordinating the search and rescue efforts, as medical teams began converging on the region to treat survivors and search for the thousands missing.

Richard Norland, the U.S. special envoy to Libya, said on the U.S. Embassy’s account on X, the platform formerly known as Twitter, that the United States “was coordinating with U.N. partners and Libyan authorities to assess how best to target official U.S. assistance.” It was not immediately clear if any international aid has reached the stricken areas yet.

Shipments of supplies, including body bags and medical equipment, left early Tuesday morning from the capital of Tripoli for the city of Benghazi, ​​the interim government in Tripoli said on its Facebook page. A medical convoy of doctors, nurses and other rescue volunteers had already arrived in Benghazi on Tuesday morning, it added. Turkish rescue teams also arrived in the city on Tuesday, according to the Libyan television channel al-Masar. Benghazi is more than 180 miles from Derna by road.

Exact figures on the scale of fatalities are difficult to obtain because search efforts continue, a spokesman for the authorities in that region said Monday evening.

Derna appeared to have suffered the worst. Local officials in the port city have declared the area a disaster zone. Roads into the city had been cut off, the City Council confirmed on Monday on its Facebook page. It called for the opening of a maritime passageway to the coastal city and for urgent international intervention.

“The situation is catastrophic,” the council said. “The city of Derna is pleading for help.”

Phone service was restored on Tuesday through one of the telecommunications companies to some areas of Derna after all communications were cut off for approximately two days.

One of the main challenges faced by Libyans affected by the disaster was the difficulty of communicating with their families and loved ones to check on their well-being. Since yesterday, Facebook posts in several groups have been filled with inquiries about the status of people there from relatives outside Derna. There was no means of communication available after the collapse of the phone networks.

The drenching rains were part of a weather front that unleashed major flooding in Greece, Turkey and Bulgaria last week, sweeping away buildings and killing more than a dozen people, before moving toward Libya.

The storm continued onward to Egypt, although its impact appeared to be less severe there. President Abdel Fattah el-Sisi of Egypt ordered the country’s armed forces to send “immediate assistance and humanitarian aid, by air and sea,” to Libya as well as Morocco, where a fatal earthquake struck on Friday.

Libya is especially vulnerable to climate change and the increasingly intense storms that warmer weather brings. Warming causes the waters of the Mediterranean to expand and sea levels to rise 2.8 millimeters a year, eroding shorelines and contributing to flooding, with low-lying coastal areas of the country at particular risk, according to the United Nations.

Nada Rashwan contributed reporting from Cairo, and Isabella Kwai from London.