More than 40 migrants have died in the Mediterranean north of Libya, the Italian navy said Saturday, while local media said they may have suffocated below decks.

“Operation underway… many migrants saved. At least 40 dead,” the navy said on Twitter, while the Corriere della Sera newspaper said those who died were found in the hold of the vessel.

The navy said because the rescue was still ongoing Saturday it couldn’t give exact numbers of dead and rescued. RaiNews24 TV, reporting from the Navy rescue coordination center in Rome, said the dead migrants were found in the hold of an overcrowded smugglers’ boat.

Europe is on track to see a record number of migrants crossing the Mediterranean this year, according to the International Organization for Migration.

In May, the Italian coastguard said it had coordinated the rescue of more than 3,300 migrants sailing across the Mediterranean Sea, but also found 17 corpses on several of the rickety boats.

The Italian authorities have in the past spoken of the harsh conditions faced by the migrants at sea, where they have to endure extreme weather changes and are at risk of hunger, thirst and violence on board.