At least three migrants died and around 25 were missing after their boat capsized at dawn near the Sicilian island of Lampedusa on Monday.
Coastguards rushed to the area 75 miles south-east of the island following an SOS call from the boat, which was making its way to Italy from the African coast amid three-metre-high waves.
According to reports, the migrants became agitated at the sight of the coastguard's ship and their reactions caused their boat to overturn.
Three bodies and 48 survivors have so far been pulled from the water.
A sea- and air-rescue operation to locate other survivors is being hampered by force 4 winds buffeting the Sicilian Channel.
Meanwhile, coastguards are escorting another boat with 350 migrants aboard towards Lampedusa, and a craft carrying 50 migrants has also been spotted making its way towards the island.
Migrants have been steadily arriving on Lampedusa since the middle of June, taking advantage of a bout of fair weather to travel to Italy from the north African coast.
Many of them risk their lives by making the crossing on small, rickety boats after paying traffickers exorbitant fees.
The vast majority of boats are intercepted off Lampedusa, which is closer to the coast of Tunisia than to the Italian mainland.
The number of would-be immigrants landing on the island has increased dramatically in recent years, with 23,000 arriving in 2005 compared to 13,000 in 2004.
On Monday Italy's Interior Minister Roberto Maroni said that Italy and Libya had already signed an agreement to patrol the Libyan coast in an effort to prevent boats from setting off, but that he needed a final green light from Tripoli.
''As soon as the Libyan government gives the go-ahead, we can start the patrols,'' he said.
''Until then, we have to control this phenomenon with the means that we have, knowing that a solution exists,'' he added.
Last month 40 people drowned and another 100 went missing when a boat taking would-be migrants capsized on its way to Italy from Libya.
At least 2,000 people die every year as they attempt to cross the Mediterranean, according to the United Nations High Commissioner for Refugees (UNHCR).
