AFP/ Rome

Around 40 people have been found dead in the hold of a migrant boat off the coast of Libya, the Swedish coastguard said Wednesday, the latest tragedy in the Mediterranean.

The macabre discovery was made after Swedish ship the Poseidon was sent to the aid of the stricken vessel by the Italian coastguard, which said rescue operations for a number of other boats were ongoing.

Swedish coastguard spokesman Mattias Lindholm told AFP the Poseidon had been able to save 439 people on the wooden boat.

"Unfortunately there were around 40 people dead in the hold," he said. "The bodies are currently being transferred to the Poseidon."

The Swedish ship was in the area as part of the EU border agency Frontex's search and rescue mission known as Triton.

Just before the discovery of the bodies, the Poseidon had picked up 130 migrants from a rubber dinghy, Lindholm said.

Italy's coastguard, which oversees rescue operations in the waters between Sicily and Libya, said a total of just under 1,900 people had been rescued by mid-afternoon but that hundreds more were still on board vessels drifting precariously off Libya.

Italian media reported that one of the boats in trouble was carrying 700 people.

MOAS, a Malta-based private organisation, said in a tweet that its boat the Phoenix was taking part in a complex rescue operation.

"Phoenix are working with Italian and Swedish vessels to assist thousands," it said.

On August 15, the Italian navy discovered the bodies of 49 migrants asphyxiated in the hold of a people smuggler's boat. Survivors later testified that the victims had been locked below deck and constrained to stay there by force.

More than 2,300 migrants have died at sea this year during attempts to reach Europe, almost invariably on overcrowded boats chartered by people smugglers.

Calm weather this week appears to have encouraged the smugglers to get as many people as possible out to sea, knowing that, in most cases, they will be picked up by Italian or international boats and taken to Italian ports.

Wednesday's rescue operations will lift to more than 110,000 the number of migrants to have landed at Italian ports this year. A further 160,000-plus have arrived in Greece triggering a crisis for which the European Union currently appears to have no solution.