At least 57 people are reported to have drowned off the Libyan coast – the latest large-scale loss of life involving migrants trying to reach Europe.
The head of the International Organisation for Migration in Libya, Federico Soda, said he was horrified.
The IOM said survivors told its staff that 20 women and two children were among those who died.
The cause of the accident near the Libyan port of Khoms is unclear.
Boats leaving Libya to Europe are usually overloaded and leave at night to evade detection by the coast guard.
Improved weather has contributed to an increase in the number of boats attempting the perilous crossing of the Mediterranean from North Africa.
An estimated 1,100 people have died so far this year more than double the figure for the same period in 2020.