Fifteen migrants have died in a boat off the Libyan coast after spending 12 days at sea without food or water, an Egyptian survivor said on Tuesday.

The owner of a beach chalet found the migrants washing up on the shore near the city of Misrata and called authorities, who brought them to the Red Crescent relief service and hospitals, residents said.

"We were 25 migrants on a boat ... We set off from (the western Libyan town of) Sabratah and we were at sea for 12 days without food and water," the survivor said. "Fifteen have died."

Residents said 10 migrants appeared to be in very poor health. No more details or comment from authorities were immediately available.

Libya’s western coast is a departure point for mainly sub-Saharan African migrants fleeing wars and poverty and hoping for new lives in Europe.

But since last year, the number of migrants reaching Italy has fallen sharply as smuggling networks inside Libya have been disrupted and the European Union has stepped up efforts to boost Libyan coastguard patrols.