A boat carrying around 250 migrants capsized between Sicily and Tunisia on Friday, leaving hundreds in the sea and some dead, the Italian navy said.
The incident came just over a week after at least 319 people drowned when a boat carrying Eritrean and Somali migrants sank near the southern Italian island of Lampedusa.
"There are at least 200 people in the sea and our helicopters are picking them up," said a navy spokesman, adding that two navy ships were assisting and dozens of survivors were being taken to Lampedusa on one of the vessels.
Maltese authorities were co-ordinating the rescue operation, which was in international waters but in a Maltese rescue zone, and a Maltese ship was on the scene, a Maltese navy spokesman said.
The boat sank only around 60 miles off Lampedusa and survivors were being taken there, he added.
The boat was seen to be in difficulty by a Maltese military plane at around 1400 GMT, which dropped a liferaft, the Maltese navy said in a statement.
Last week's disaster was one of the worst in a long migrant crisis that has seen tens of thousands of people arrive in flimsy, overcrowded boats in southern Italy, and some vessels wrecked. Lampedusa, a tiny island midway between Sicily and Tunisia, has borne the brunt.
According to the United Nations High Commissioner for Refugees, 32,000 have arrived in southern Italy and Malta this year alone, around two thirds of whom have filed requests for asylum.
Earlier on Friday at least 500 more migrants in at least three separate boats arrived or were rescued on the way to different parts of Sicily.
Most migrants come from sub-Saharan Africa, but this year many are fleeing the Syrian civil war or political turmoil in Egypt and other parts of North Africa. Many are drawn by hopes of finding work in Europe and often do not stay in Italy.
(Additional reporting by Antonella Cinelli, Chris Scicluna and Philip Pullella; writing by Gavin Jones; editing by Andrew Roche)