A migrant boat capsized in the Mediterranean today, an Italian coastguard spokesman said, and 88 people have been rescued while the number of possible dead is unknown.

It was the second shipwreck in two days, after five were confirmed to have died when a large fishing boat flipped over in the sea on Wednesday.

Boat arrivals in Italy have risen sharply this week amid warm weather and calm seas, and about 20 rescue operations are currently under way, the spokesman said.

Between 20 and 30 people are feared dead, Ansa news agency reported without saying where it got the information, while the coastguard declined to estimate how many may have died.

"We don't know how many people were on board," the coastguard spokesman said.

An aircraft from the European Union's Sophia mission to fight people smuggling spotted the overturned vessel and called in the coastguard to assist in the rescue.

The coastguard has coordinated the rescue of around 900 migrants in seven different operations on Thursday. That brings the total of migrants who have been rescued since Monday to more than 7,000.

Through Tuesday, total sea arrivals in Italy had fallen by nine per cent this year, to 37,743, according to the Interior Ministry, but the country's migrant shelters are already under pressure to house 115,507 migrants, about twice as many as two years ago.

Some 650 migrants are scheduled to arrive in the Sicilian city of Porto Empedocle later on Thursday, including the five dead bodies recovered by the Italian navy on Wednesday.

In the past two years, more than 320,000 boat migrants have arrived on Italian shores and an estimated 7,000 died in the Mediterranean as they sought to reach Europe.