The Geo Barents ship, run by charity Doctors Without Borders (MSF), took onboard 558 people, mainly Africans, in eight separate operations off the coast of Libya in the last 11 days, the charity said.
They include 174 minors and a woman who is eight months pregnant.
The German charity boat Sea Watch 3 is also seeking a port to disembark 440 migrants it rescued in recent days in the Mediterranean, including women and young children.
“The weather deteriorates … Everyone has the right to disembark, now,” Sea Watch wrote on Twitter.
Italy has seen a sharp increase in boat migrants in recent months with the government struggling to secure an agreement with European Union partners over how to deal with the influx.
As of Dec. 28, 66,482 migrants have reached Italy so far this year against 34,134 in the same period of 2020, interior ministry data show.