Benghazi, Lybia - The death toll from freak floods in eastern Libya is expected to soar dramatically, with 10,000 people reported missing, the Red Cross warned on Tuesday.

Officials in Libya have said at least 150 people were killed in the sudden flooding on Sunday afternoon after Storm Daniel swept the Mediterranean, lashing Bulgaria, Greece, and Turkey.

But Tamer Ramadan of the International Federation of Red Cross and Red Crescent Societies (IFRC) said the actual toll was likely to be many times higher.

"Our teams on the ground are still doing their assessment (but) from what we see and from the news coming to us, the death toll is huge," he told reporters in Geneva via video link from Tunis.

"It might reach to the thousands," he said in English. "We don't have a definite number right now."

Independent sources had told the IFRC the number reported missing was "hitting 10,000 persons so far".

"The humanitarian needs are much more beyond the abilities of the Libyan Red Crescent and even the abilities of the government," Ramadan said.

"That's why the government in the east has issued an international appeal for support," he said, adding that IFRC was also preparing to launch an emergency appeal for funds towards the response.

World Health Organization spokeswoman Margaret Harris meanwhile described the situation in Libya as "a calamity of epic proportions".

Experts have described Storm Daniel – which killed at least 27 people when it struck parts of Bulgaria, Greece, and Turkey in recent days – as "extreme in terms of the amount of water falling in a space of 24 hours".

In eastern Libya, the storm hit the coastal town of Jabal al-Akhdar especially hard, as well as Benghazi, where a curfew was declared and schools closed for several days.

The United Nations' World Meteorological Organization (WMO) meanwhile described how "entire neighborhoods" in Derna had disappeared and their inhabitants been "swept away by water, after two aging dams collapsed making the situation catastrophic and out of control".

Speaking on Libyan network Almasar, Oussama Hamad, prime minister of the east-based government, has reported "more than 2,000 dead and thousands missing" in the city of Derna alone.

Hamad's government – which in war-battered Libya rivals a UN-brokered, internationally recognized transitional administration in Tripoli – has declared Derna a "disaster area".