The United Nations said on Wednesday that 42 people were missing and presumed dead after a rubber boat capsized off the Libyan coast last week.
It was the latest in a series of similar disasters in a stretch of the Mediterranean Sea that has claimed the lives of more than a thousand people so far this year.
Only seven survivors were rescued after six days adrift, said a statement from the UN's International Organization for Migration.
The vessel, carrying 47 men and two women, left Zuwara, west of Tripoli, on November 3, but around six hours later, high waves caused the engine to fail, said the IOM.
The boat capsized, throwing all passengers overboard, the statement added.
On Saturday, the Libyan authorities carried out a search and rescue operation near Al Buri oil field.
"After drifting at sea for six days, only seven men — four from Sudan, two from Nigeria, and one from Cameroon — were rescued," the IOM said.
"Tragically, 42 individuals remain missing and are presumed dead, including 29 from Sudan, eight from Somalia, three from Cameroon, and two from Nigeria."
IOM staff gave the survivors emergency medical care, food and water once they were brought ashore.
More than 1,000 people have died this year attempting the main central Mediterranean crossing between North Africa and southern Europe, according to IOM figures.
"With this latest shipwreck, the total has risen even further, reinforcing the urgent need for strengthened regional cooperation, expanded safe and regular migration pathways, and more effective search and rescue operations to prevent further loss of life," the IOM said.
