At least 43 people died after their boat sank early on Sunday morning off the Italian coastal city of Crotone in the southern region of Calabria, according to Italian media.
Forty-three bodies have been recovered, according to the Italian coastguard.
The search for survivors is being hampered by stormy seas.
Rescuers say about 80 people have been saved.
Reports say the migrants' vessel was overloaded and appeared to have split apart because of the violent waves.
The vessel is reported to have been carrying more than 200 people.
"Dozens and dozens of people drowned, including children. Lots missing. Calabria is in mourning after this terrible tragedy," regional governor Roberto Occhiuto said.
The tragedy comes just days after the hard-right government in Rome pushed through parliament a controversial new law on rescuing migrants.
Prime Minister Giorgia Meloni, the leader of the post-Fascist Brothers of Italy party, won power in October, partly on a promise to stem the flow of migrants reaching Italian shores.
Meloni on Suday morning expressed "deep sorrow" for the incident, blaming the deaths on traffickers.
"It is inhumane to exchange the lives of men, women and children for the price of the 'ticket' they paid in the false perspective of a safe journey," she said in a statement.
"The government is committed to preventing departures, and with them the unfolding of these tragedies, and will continue to do so."
The new law obliges migrant aid vessels to make just one rescue attempt at a time. Critics say the legislation risks increasing the number of drownings in the central Mediterranean.
The interior ministry says nearly 14,000 migrants have arrived in Italy by sea so far this year, up from 5,200 over the same period last year and 4,200 in the first two months of 2021.
According to estimates by monitoring groups, more than 20,000 people have died or gone missing at sea in the central Mediterranean since 2014.
