Emergency response teams and relief goods have been deployed from France, Iran, Malta, Russia, Tunisia, Turkey and the United Arab Emirates, with more on the way from multiple other European and Arab nations.
The aid effort has been hampered by the political division of Libya, which was thrown into war and chaos after a 2011 NATO-backed uprising led to the overthrow and killing of veteran dictator Moamer Kadhafi.
The oil-rich North African country now remains split between two rival governments – a UN-backed administration in the capital Tripoli, and one based in the disaster-hit east.
Amid the chaos, the true death toll remained unknown, with untold numbers feared swept into the sea.
The health minister of the eastern administration, Othman Abdeljalil, has said that 3,252 people were confirmed dead in Derna, where corpses wrapped in blankets and in body bags have lined squares and streets.
The UN Office for the Coordination of Humanitarian Affairs warned on Sunday that the eventual death toll from Derna alone could be as high as 11,300, with another 10,100 missing.
But the Libyan Red Crescent, which was cited by the UN agency, earlier denied a UN death toll of over 10,000 and called on the media to “exercise caution and accuracy”.
The massive flood came as Libya was lashed on Sep 10 by the hurricane-strength Mediterranean Storm Daniel, which had earlier brought deadly floods to Greece, Turkey and Bulgaria.
The rapidly rising waters burst two upstream river dams in Derna, sending a late-night tidal wave crashing through the centre of the city of 100,000, sweeping entire residential blocks into the Mediterranean.
UN experts have blamed the high death toll on climatic factors as the region has sweltered under an unusually hot summer, and the legacy of Libya’s war that has depleted its infrastructure, early warning systems and emergency response.
Questions are being asked about whether the disaster could not have been prevented when cracks in the dams have been reported since 1998.