The interior ministers of Germany, France and Italy are due to meet for crisis talks in Paris amid a warning from Italy that the influx of migrants into the country is unsustainable.
Italy has threatened to close its ports and impound rescue ships run by aid agencies carrying people from Libya.
It needs more support as people cross the Mediterranean from Africa in large numbers, the UN’s refugee agency said.
Over 500,000 migrants have passed through Italian ports since 2014.
The Italian government has demanded action from other countries within the European Union following the arrival of 12,000 migrants in the space of just two days last week.
“What is happening in front of our eyes in Italy is an unfolding tragedy,” the UN High Commissioner for Refugees Filippo Grandi said.
“This cannot be an Italian problem alone,” he added.
The coastguard in Rome currently co-ordinates rescue missions in the area, but the Italian government said that other European countries should take in some of the huge number of migrants making the journey from Africa.
Aboard the Mediterranean’s migrant rescue boats
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On Thursday, the EU’s migration commissioner, Dimitris Avramopoulos, promised more financial support for Italy, and urged member states to demonstrate greater solidarity.
Mr Grandi said 12,600 migrants and refugees had arrived in Italy last weekend alone.
In total, he said, 83,650 people have reached Italy by sea since the beginning of the year – a 20% increase on the same period in 2016.
An estimated 2,030 have lost their lives in the Mediterranean this year.
The vast majority of migrants making their way to Italy across the Mediterranean set off from Libya.
Libya is a gateway to Europe for migrants from across sub-Saharan Africa and also from the Arabian peninsula, Egypt, Syria and Bangladesh. Many are fleeing war, poverty or persecution.
The UNHCR said that among the arrivals in Italy there was an alarmingly high rate of unaccompanied children or victims of sexual or gender-based violence.