Italy was struggling on Monday to accommodate arrivals from North Africa and the Balkans as the country's Red Cross called for more international efforts against migration "chaos".
On Lampedusa island, Italy's southernmost outpost, more than 4,200 people landed over the weekend, local police chief Emanuele Ricifari told Reuters.
He said that despite the "record numbers" the authorities were in control of the situation.
In Trieste, near the border with Slovenia, Mayor Roberto Dipiazza was less sanguine as he complained to the Corriere della Sera daily about an unprecedented "invasion of migrants".
"I have been dealing with problems related to migrants since the 1990s, I have seen everything and more, but I could not imagine such a thing. The city is in an emergency," he said.
Italy has recorded more than 107,500 sea arrivals in the year to date, compared with around 53,000 in the same period last year.
The spike has partly been driven by an increase in the ranks of unaccompanied minors making the perilous sea journey to Italy. More than 12,000 have arrived since Jan. 1.
In Lampedusa, incoming sea migrants are crammed in a so-called "hotspot" with an official capacity of a few hundred places, before being transferred to the larger island of Sicily.
The facility is routinely overcrowded, with Italian news agencies reporting on Monday that it was hosting nearly 3,600 migrants.
The Italian Red Cross (CRI) took over the running of the facility on June 1, replacing a cooperative that had been criticised for failing to provide adequate care.
CRI President Rosario Valastro called on Facebook for "a different way of welcoming and different migration policies".
"I hope that not only Italy but the whole European and international community will be able to respond effectively and not give in to chaos," he said.
The Italian government has vowed to go after human smugglers and has restricted the activities of charity rescue ships, impounding three of their vessels last week.
But with the country facing a shrinking population and labour force shortages, it has also raised entry quotas for non-EU migrant workers to 452,000 for 2023-2025 from around 83,000 in 2022.
(Reporting by Alvise Armellini, editing by Gavin Jones and Alex Richardson)