The Italian coastguard says three separate operations saw hundreds of people rescued from inflatable boats.
The migrants were rescued in three separate operations on the sea the crossing between Libya and Italy.
Considered the deadliest crossing in the world, the stretch of water has become a route for hundreds of thousands of people attempting to reach Europe from North Africa.
Since 2014 more than 14,500 people are known to have died in the central Mediterranean, and in 2017 one in 36 attempting to cross the water perished.
All of those rescued in Friday's operation were aboard inflatable boats, the coastguard said.
Sea Watch, a rescue NGO named by the coastguard as one of the organisations involved in the rescue, tweeted that it had rescued approximately 300 people out of two rubber boats in distress.
In its statement the coastguard said that the Sea Watch vessel could not reach the Italian port, however, "due to the deterioration of the weather conditions, the number of migrants on board and the absence of sufficient water, food".
Italy has recently upped its efforts to prevent migrants reaching its shores, with EU-backed missions encouraging the Libyan coastguard to pick up boats and imposing new rules on NGOs running rescue missions.
It means the number of people reaching Italy via the central Mediterranean route has dropped: in the first three months of this year 6,296 people were recorded as arriving in Italy, compared to 24,292 in the same period in 2017.
A UNHCR statement said "greater engagement of the Libyan Coast Guard in search and rescue operations in the Central Mediterranean has likely contributed to lesser arrivals in Italy compared to last year".
But the involvement of Libyan authorities has led to grave problems, with migrants returned to Libya where they have been placed in detention camps and exposed to further danger, people trafficking and abuse.
Sky News last year recorded scenes of beating, slavery and starvation at detention centres, and the desperate situation in Libya means some people have been returned to the countries they left.