More than 330 migrants rescued by Italian coast guard and other European vessels have already disembarked at Sicilian ports, Italian media reported.
Another hundred were en route to the western city of Trapani on Monday while 450, including a woman about to give birth, are due to arrive in Augusta by evening aboard the Aquarius, a boat operated by charity group SOS Mediterranee along with Doctors Without Borders.
UPDATE: After rescuing 115 people yesterday, #Aquarius team has been engaged in multiple transfers until late this afternoon. In collaboration with @openarms_fund, 335 more were welcomed on board, including a pregnant Eritrean in labour. Aquarius is now heading back to #Italy. pic.twitter.com/uecIFL2SeH— MSF Sea (@MSF_Sea) December 10, 2017
"Testimonies gathered Sunday aboard the Aquarius reflect the extreme gravity of the situation in Libya for migrants and refugees, who lacking a safer alternative, risk their lives at sea to escape what they call the Libyan hell," said Francis Vallat, the SOS Mediterranee president in France.
"Today, the absolute priority is to rescue at sea those who continue to flee and to accompany them to a safe place where they will be protected and where their basic human rights will be respected".
Libya has long been a major transit hub for migrants trying to reach Europe.
More than 3,000 have died attempting to cross the Mediterranean in rickety boats, according to the International Organization for Migration. Others have fallen prey to serious abuse at the hands of traffickers and others.
Recent shocking footage by US news channel CNN appeared to show migrants being sold as slaves near Tripoli, sparking global outrage and promises from the African Union it would repatriate 20,000 distressed migrants in the next six weeks.
"I would rather die than return to prison," a 25-year-old from Cameroon said, according to SOS Mediterranean.
"In the cell they hit us, they tied our feet and hands, feet up, head down. Europeans would come visit, and the guards would tell us not to talk."
Nicola Stalla, relief coordinator for SOS Mediterranee, said weather conditions are also a concern for migrants, but what "they fear more than anything is be intercepted and sent back to the hell they came from in Libya".
The number of migrants and refugees who have arrived in Europe this year – nearly 164,000 – is less than half of last year's total of 348,000.
The flow has been stemmed by controversial deals between the EU, Turkey and Libya.