Between 130 and 250 people were missing and at least 15 appeared to be dead after a boat carrying refugees from Libya capsized south of Sicily early on Wednesday, coast guard officials and aid workers said.
Rescuers picked up 47 people, including a heavily pregnant woman after the overloaded boat, which left Libya two days ago, sank at about 4:00 am (0200 GMT) 40 miles (64 km) south of the island of Lampedusa.
According to the International Organisation for Migration (IOM), a migrant assistance agency which has officials on Lampedusa, an Italian fishing boat rescued another three people.
Between 15 and 20 bodies were seen in the water, officials said but high winds and rough seas made it difficult for coast guard boats and a police helicopter to operate.
Coast guard officials said the boat had originally been carrying around 200 people but the IOM put the figure as high as 300, of whom it said some 250 were missing.
The incident provided a stark illustration of the dangers run by desperate people who pay about 1,000 euros ($1,427) for a place on one of the overloaded fishing vessels carrying refugees and migrants from Africa.
"The vessel, which was laden beyond capacity, had left the Libyan coast with migrants and asylum seekers from Somalia,
Nigeria, Bangladesh, Cote d'Ivoire, Chad and Sudan," IOM said in a statement. "Some 40 women and 5 children were on board. Only two women survived the shipwreck."
On Monday, the United Nations refugee agency said more than 400 people fleeing Libya on two boats were missing.
Thousands have crossed so far this year after the collapse of the former Tunisian regime and fighting in Libya brought down strict border checks that had previously barred the way into Europe.
Most have been young men from Tunisia, seeking to get to France but in recent days there have been growing numbers of arrivals from Libya, underscoring Italian fears the fighting there could set off a new exodus.
IOM said that 2,000 mostly African migrants and asylum seekers had landed in Lampedusa from Libya in the past 10 days.
Lampedusa, roughly midway between Sicily and Tunisia, has been the focal point for the crisis, with some 20,000 illegal migrants arriving this year and overwhelming the infrastructure of the tiny island, which normally lives on fishing and tourism.
Thousands were forced to shelter in makeshift tent camps until Italian Prime Minister Silvio Berlusconi sought to end the weeks-long emergency by sending ferries to clear the island.
However, that has simply shifted the problem to other areas in Italy and caused arguments among regional governments over where to set up migrant holding centres.
Italy has also been at odds over the issue with France, which has turned back migrants trying to cross the border. Berlusconi is due to meet French President Nicolas Sarkozy on April 26 in Rome, when the issue will probably be discussed.
On Tuesday, Italian interior minister Roberto Maroni signed an agreement with the Tunisian government to try to halt the flow, pledging aid, increased police cooperation and possible compulsory repatriation for illegal immigrants.
The accord was confirmed on Wednesday by a cabinet meeting in Rome which set up an inter-ministerial contact group to monitor progress.