At least 40 migrants have died in the hold of an overcrowded smuggling boat in the Mediterranean north of Libya, apparently killed by fuel fumes.
Some 320 others aboard were saved by the Italian navy, the rescue ship's commander said.
"The dead were found in the hold," said Cmdr Massimo Tozzi, from the navy ship Cigala Fulgosi while the rescue was continuing. Asked how the migrants died, he said "it appears to be from inhaling exhaust fumes".
When rescuers stepped aboard, the bodies of migrants were "lying in water, fuel, human excrement" in the hold, Cdr Tozzi said.
The death toll was not yet final. "They are still counting the victims," Interior Minister Angelino Alfano told reporters.
Cdr Tozzi said the survivors included three children and 45 women, some of whom "were crying for their husbands (and) their children who died in the crossing".
The navy said that the survivors were later transferred to a Norwegian ship with the Frontex mission, a European effort to save migrant lives in the Mediterranean. The survivors were being brought to a southern Italian port.
Elsewhere in the Mediterranean, migrants on a Turkish beach scuffled over places on one inflatable dinghy and frantically bailed out another to keep it from sinking during a dramatic night that highlighted their desperation to reach the Greek island of Kos - and the safety of Europe.
The scenes, captured early on Saturday by Associated Press journalists on a moonless night, came as Turkish authorities reported that 2,791 migrants have been caught in the Aegean Sea in the past five days alone, most of them Syrians.
Kos is only four kilometres (2.5 miles) from Turkey at its closest point, its twinkling lights at night an irresistible beacon to those fleeing war or poverty.
An Italian navy admiral coordinating the sea rescue missions said the first rescuers, in two rubber dinghies, approached the boat carefully, since often migrants rush to one side of their vessel when they spy help and the boat capsizes.
"We saw this boat filled up to unimaginable levels," Admiral Pierpaolo Ribuffo said.
So far, at least seven of the bodies had been transferred to the rescue vessel, which was headed toward Sicily.
An estimated 2,300 migrants have died at sea this year trying to make the crossing, according to figures released by the International Organisation for Migration. The Libya-to-Italy route is by far the deadliest. The exact toll of dead will never be known, as some smuggling boats are believed to have gone down at sea without rescuers being aware of them.
The number of migrants trying to reach Europe by sea is on track to hit a record this year, according to the IOM. Greece has reported 134,988 arrivals from Turkey this year.
Mr Alfano told a news conference that as of Saturday, 103,000 migrants had been rescued at sea and brought to Italy in operations coordinated by the Italian coast guard. Along with a few other migrants landing in Spain and Malta, that means more than 243,000 people have crossed so far this year, compared to 219,000 for all of 2014.
In Libya, smugglers have taken advantage of the increased chaos and fighting among the North African nation's tribes and militias, some of whom are loyal to the Islamic State group.