About 6,055 migrants were rescued on Monday as they tried to reach Europe on about 40 boats, one of the highest numbers in a single day, Italy's coast guard said.
A spokeswoman said at least nine migrants had died and a pregnant woman had been taken by helicopter to a hospital on the Italian island of Lampedusa, halfway between Sicily and the Libyan coast.
One coast guard ship rescued about 725 migrants on a single rubber boat, one of some 20 rescue operations during the day.
Three are still under way and the spokeswoman said the number saved could reach 6,000 by the end of the day.
About 10 ships from the coast guard, the navy and humanitarian organisations were involved in the rescues, most of which took place some 30 miles off the coast of Libya.
The LÉ Samuel Beckett is involved in the search and rescue operation, and earlier on Monday – following a request from the Italian Maritime Rescue Co-Ordination Centre – the Irish naval ship located and rescued 128 people during two search and rescue operations.
The first rescue operation commenced at 8.30am where 19 migrants were rescued from the water 42 nautical miles NE of Tripoli. In a second operation, 109 migrants were rescued from a rubber craft and brought on board LÉ Samuel Beckett.
Monday was the third anniversary of the sinking of a migrant boat off Lampedusa in which 386 people died.
According to the International Organisation for Migration, around 132,000 migrants have arrived in Italy since the start of the year and 3,054 have died.