The death toll in the coastal city after Mediterranean storm Daniel unleashed the massive flood - fed by the breaching of two dams in heavy rains - has eclipsed 11,000 and more than 10,000 are missing.
Five days on, searchers are still digging through mud and hollowed-out buildings in Derna, looking for bodies.
According to a war monitoring group, the Britain-based Syrian Observatory for Human Rights, 42 Syrians have been confirmed dead in Libya while the real number could be as high as 150.
The victims include both Syrians who were living and working in Libya long term, and Syrian migrants who were using Libya as a transit point in efforts to reach Europe, most often by way of perilous voyages across the Mediterranean Sea, in unsafe boats organised by smugglers.
As the storm pounded Derna late Sunday, residents said they heard loud explosions when the dams outside the city collapsed.
Floodwaters washed down Wadi Derna, a river running from the mountains through the city and into the sea.
Rami Abdurrahman, who runs the Observatory, said he has not been able to confirm a single survivor out of the 150 Syrians missing in Derna since Sunday night.
But definite numbers are hard to come by in the chaotic aftermath of the destruction.
Like Syria, where the civil war has killed half a million people and forced more than five million to become refugees around the world, Libya has been through its own years of conflict.
The oil-rich North African country has been split between rival governments in the east and west since 2014, backed by various militia forces and international patrons.
Derna is governed by Libya's eastern administration, where military commander Khalifa Hiftar wields significant power.
Still, for some Syrians, Libya offered prospects of a better life.
Syrians can easily get into Libya on a tourist visa and find work - wages are higher than what many earn at home.
Zeid Marabeh, 19, came to Libya two years ago from the central city of Homs and worked as a carpenter.
He recounted to The Associated Press over the phone from Derna how he watched water surging toward his building on Sunday night.
"Then I heard a loud boom," Marabeh said.
It was the moment the dams collapsed.
When water levels started rising in his neighbourhood, he frantically ran toward higher ground - the nearby Eastern Shiha hill.
From there, he saw the water destroy almost everything in its path.
After the waters subsided, he went back on Monday morning to check on his uncle and relatives.
The building where they lived had disappeared.
He said his uncle, Abdul-Ilah Marabeh, his aunt Zeinab and their one-year-old daughter Shahd were gone.
Marabeh said he looked through the rows of bodies laid out on their street but could not find his uncle's family.
