Some 600 migrants rescued at sea arrived on Friday in Sicily.
It is one of the biggest influxes since Italy struck a deal with Libyan authorities to limit migrant smuggling, raising concerns of a renewed surge on the Libyan human trafficking corridor.
The migrants, including many unaccompanied minors from sub-Saharan Africa, were rescued in seven operations over 36 hours, and transported on Friday to Palermo by the German non-governmental organisation SOS Mediterranee.
They came as three weeks of fighting around the Libyan city of Sabratha has destabilised militias that pledged to help reduce the flow of migrant smuggling across the Mediterranean Sea, leaving many migrants and refugees displaced.
SOS Mediterranee president Valeria Calandra told Sky TG24 the renewed instability in Libya has only increased the desire of migrants to escape the lawless North African country.
"It was very improbable that from today to tomorrow you can stop everyone," she said.
"I think this rescue is the first of many others that will arrive."
The number of migrants dropped dramatically in July and August, before a surge from 3,914 in August to 6,288 in September.
Still, September arrivals were two-thirds below last year's total for the same month, and the 2,800 arrivals so far this month are well below the 12,400 in the same period last year.
A spokesman for the UN refugee agency in Rome, Federico Fossi, said it was too early to say what is driving the recent surge and if it will be sustained.
He noted that even the deal with Libyan forces to stanch the flow of migrants never fully stopped the smugglers' boats.
"In last few days, there has been a light increase. We need to see over the medium-term if there is a new trend," he said.
The UNHCR said on Friday that fierce clashes over the last three weeks near Sabratha, some 50 miles west of Tripoli, have stranded 3,000 Libyan families, most of whom have since returned home, and displaced more than 10,000 refugees and migrants, who remain "in need of urgent assistance".
After taking control of detention centres that had been run by migrant traffickers, Libyan authorities transferred 4,500 migrants to a hangar in the Dahman area and others to detention centres near Tripoli, the refugee agency said.
UNHCR said it was sending emergency assistance including sleeping bags, hygiene kits, food and blankets to Libya.
Many migrants were found without clothing or shoes, had suffered injuries requiring urgent medical care or were severely traumatised and in need of psychological support, the refugee agency said.
"'Overall, our team on the ground paint a very grim picture," UNHCR said.