More than 5,000 migrants were saved on Tuesday and Wednesday off the Libyan coast and 28 bodies recovered, bringing the total number of people rescued this week to more than 11,000, Italy's coast guard said.
More than 20 people were reported to have suffocated in the hold of one overloaded fishing boat, bringing the total death toll for Monday and Tuesday to 50.
Italian officials said three women saved on Monday had given birth over the past 24 hours on a coast guard vessel that was bringing some 1,000 refugees to Sicily. The women and their three children were all reported to be in good health.
The coast guard said the 4,655 migrants rescued on Tuesday were taken from 33 overcrowded boats, including 27 rubber dinghies and one wooden boat that was believed to have been carrying around 1,000 people.
More than 6,000 migrants were rescued on Monday, but on Wednesday the number fell sharply to about 368 from six different boats, the coast guard said.
A photographer working for Agence France-Presse, who was aboard a ship chartered by a Spanish non-governmental organisation to help with the rescue missions, was quoted as saying he had counted 22 bodies on that boat. He told Italian media he thought other corpses were still in the hold.
At its closest, Libya is 290 km (180 miles) from the Italian island of Lampedusa and people smugglers have taken advantage of the chaos in the north African state to use it as their main staging post in the region for journeys to Europe.
"Obviously the good weather has played an important role in explaining the large number of recent arrivals," a coast guard spokesman said.
The latest surge in new arrivals means at least 142,000 migrants have reached Italy since the start of the year and around 3,100 have died making the perilous trip. An estimated 154,000 came to Italy in 2015 and 2,892 died.
The vast majority of refugees come from Africa, including Nigeria, Eritrea, Guinea, Gambia, Sudan, Ivory Coast and Somalia.
The migrants are brought to Italy, where EU and Italian officials work together to identify and fingerprint the asylum seekers. European law says migrants must stay in the country where they first enter the bloc and Italy is increasingly struggling to deal with the growing numbers.
As part of a deal to relieve pressure on Europe's frontline states in the migration crisis, the European Commission last year devised a plan aimed at moving thousands of new arrivals away from Italy and Greece towards other EU members.
Under the scheme, up to 40,000 migrants could be relocated from Italy over two years, but so far only a few hundred have been flown out with many EU allies reluctant to welcome in asylum seekers and refugees.
(By Crispian Balmer; Additional reporting by Steve Scherer; Editing by Janet Lawrence)