Some 46,100 migrants have crossed the Mediterranean to reach Italy so far this year, with almost a third of them arriving last week alone, according to the United Nations Refugee Agency.

The total up to Sunday was equivalent to the same period in 2015, with about 14,000 arriving last week, UNHCR spokeswoman Carlotta Sami said in a telephone interview. More than 700 migrants perished in three shipwrecks last week.

"We expect a slight increase in coming weeks," Sami said. "We’re concerned that crossings are concentrated in certain weeks, which makes it difficult for rescue services to help people."

As yet there is no indication that migrant flows are shifting to the central Mediterranean from the Aegean route from Turkey to Greece after the effective closure of the route following the European Union accord with Turkey.

Those making the crossing to Italy mostly originate from the Horn of Africa and sub-Saharan Africa, with a very small number of Syrians.

Sami added that migrants are increasingly setting out from Libya aboard fishing boats packed with up to 550 people as opposed to rubber dinghies mostly used so far.