More than 1,400 migrants arrived on the Italian island of Lampedusa at the weekend, media reports said.
The mass landings sparked calls from far-right politicians for action to stem the flow, amid fresh moves by Italian authorities against the rescue boats who operate in the central Mediterranean.
Some 15 boats arrived on Lampedusa from Saturday night onwards, Italian news agencies said -- one of them with almost 400 people of different nationalities on board, including 24 women and children.
The arrivals were condemned by Matteo Salvini, leader of the far-right League party who is facing trial in Sicily for refusing to allow migrants to disembark while he was interior minister in August 2019.
"With millions of Italians in difficulty, we cannot think of thousands of illegal immigrants," he said, demanding a meeting with Prime Minister Mario Draghi to discuss the issue.
Charity Alarm Phone meanwhile appealed for help to pick up five boats carrying more than 400 people in distress in Maltese waters, warning: "The situations on board are critical... Rescue is needed now!"
Italy is a prime entry point for Europe-bound migrants, and more than half a million people have landed on its shores since the start of 2015, according to the International Organization for Migration (IOM).
The stretch of water between Sicily and North Africa is also one of the world's deadliest migration routes.
Between January 1 and April 21 this year, 8,604 people arrived in Italy and another 65 in Malta, while 359 people died, the IOM says.
Numerous charity ships operate in the area, trying to save those who end up in the water after crossing in packed or leaky boats. Some activists accuse authorities of letting them drown.
But the NGOs in turn have faced accusations of colluding with Libyan migrant traffickers to bring people to safety on European shores -- charges they strongly deny.
Judicial authorities in Sicily this weekend reinstated a detention order against the Sea-Watch 4 vessel, run by Germany's Sea-Watch organisation, which had kept it in Palermo for six months until March, media reports said.
The order followed a safety inspection that found too many life jackets on board, saying the ship's sewage system was insufficient for the potential number of people rescued.
Activists claim the inspection was a smokescreen to block the ship.
Another vessel, Sea-Watch 3, was impounded by the Italian coastguard in March in the Sicilian port of Augusta, again over safety issues.