At least 61 migrants including a baby died when their overcrowded boat smashed into rocky reefs and broke apart off the Italian coast before dawn on Sunday.
The wooden gulet, a Turkish sailing boat, was carrying up to 250 people when it crashed into a rock near Calabria in the south of the country.
Initial reports claimed the vessel split in two because of its heavy load and rough seas, but survivors have told rescuers there was an explosion on board.
One survivor was arrested on migrant-trafficking charges, the Guardia di Finanza customs police said.
On Monday Pakistan Prime Minister Shehbaz Sharif said more than two dozen Pakistanis were believed to be among those who drowned.
“The reports of the drowning of over two dozen Pakistanis in a boat tragedy in Italy are deeply concerning and worrisome,” Mr Sharif said. “I have directed the foreign office to ascertain facts as early as possible and take the nation into confidence.”
Pakistan Foreign Ministry representative Mumtaz Zahra said details had been requested from Italian authorities for.
Cutro's Mayor, Antonio Ceraso, said women and children were among the dead. Exact numbers as to how many children had died were not yet available.
His voice cracking with emotion, Mr Ceraso told the SkyTG24 news channel that he had seen “a spectacle that you would never want to see in your life … a gruesome sight … that stays with you for all your life”.
The vessel was reported to have left Izmir in eastern Turkey three or four days ago, and survivors said about 140 to 150 were on board the 20-metre boat.
Other estimates suggested between 200 and 250 people were on board.
The survivors were mostly from Afghanistan, as well as a few from Pakistan and a couple from Somalia.
“Many of these migrants came from Afghanistan and Iran, fleeing conditions of great hardship,” Italian President Sergio Mattarella said.
It comes just weeks after MPs approved legislation to restrict sea rescues, with captains risking a €50,000 ($52,800) fine if found in breach of the new rules.
European Commission President Ursula von der Leyen on Sunday called for progress on a stalled reform of EU asylum rules after the tragedy.
Ms Von der Leyen tweeted that the deaths earlier on Sunday were a “tragedy” that left her “deeply saddened”.
“We must redouble our efforts on the Pact on Migration and Asylum and on the Action Plan on the Central Mediterranean,” she said.
European border agency Frontex, which has an €11 billion ($12 billion) budget for 2021 to 2027, receives almost real-time, high-resolution monitoring images from the EU's Copernicus satellite and airborne monitoring system.
Frontex runs Operation Themis, the mission of which is to “support Italy with border control, surveillance and search and rescue in the Central Mediterranean”.
The boat was seen on Saturday 65km off the coast by aircraft from the agency.
Boats also often leave from Libya, undertaking the deadliest route across the Mediterranean, which has claimed the lives of more than 17,000 people since 2014, according the International Organisation for Migration.
“There have been landings but never a tragedy like this,” Mr Ceraso told RAI. “The sea keeps returning the bodies. It's something you would never want to see.”
Pope Francis said he was praying for all those involved in the tragedy, during his weekly address in St Peter's Square.
Italian MPs recently approved legislation proposed by Prime Minister Giorgia Meloni's right-wing government to impose stricter rules on charities rescuing migrants at sea.
Under the new rules, charity ships must request a port and sail to it “without delay” after a rescue, rather than remain at sea looking for other migrant boats in distress.
The new legislation is a call “to let people drown”, rescuers have previously told The National.
Ms Meloni assumed power in October pledging to curb migration to Italy.
She expressed “deep sorrow” over Sunday's incident but vowed to crack down on migrant crossings.
Interior Minister Matteo Piantedosi said it was a huge tragedy “which shows the absolute need to act firmly against irregular migration channels”.
In December, Ms Meloni said the EU must do more to halt migrant flows into Italy, adding that the country “should not do alone what others are not willing to do”.
Her deputy visited Tunisia last month to discuss migration and said Italy would accept more “legal migrants” if Tunis took action to reduce crossings from its shores.