Rescue ships in the Mediterranean were searching for survivors late Wednesday off the coast of Libya where a boat carrying hundreds of migrants capsized, according to authorities and aid agencies.
Only about half of the estimated 600 migrants on board the vessel are believed to have been rescued, according to Doctors Without Borders, the international aid group, which dispatched rescue ships to the site.
"It was a horrific sight, people desperately clinging to life belts, boats, and anything they could, fighting for their lives, amidst people drowning, and those who had already died," Juan Matias, the group's project coordinator on Dignity I, one of its search and rescue ships, said in a statement.
The capsizing was the latest of many involving migrant ships, as Europe's migration crisis shows no signs of abating.
The Italian coast guard was coordinating a multinational rescue effort that includes craft from Italy, Ireland and private aid agencies.
An Italian coast guard officer, Capt. Filippo Marini, told the Associated Press that about 400 migrants had been rescued and 25 bodies recovered from the sea. It was not possible to reconcile the discrepancies between his account and that of Doctors Without Borders.
There was no official word on why the boat sank. However, overcrowded and unseaworthy vessels ferrying would-be immigrants frequently tip over in the sea between Libya and Italy, a zone that authorities call the world's deadliest border corridor.
More than 2,000 migrants have perished trying to cross the Mediterranean this year, according to the International Office for Migration, a Geneva-based intergovernmental group. About 188,000 have been rescued, the group said in a study released this week.
Tens of thousands more are waiting to make the illicit and perilous trip from Libya, a hub for sub-Saharan Africans and others seeking to enter Europe without documents.
Many Europe-bound migrants find passage in overcrowded fishing craft and rafts organized by Libya-based smuggling syndicates.
In the deadliest incident in recent years, a fishing boat from Libya carrying as many as 800 migrants sank in April; only 27 survived, authorities said.
Many victims on that boat were trapped below deck as the vessel tipped and went down quickly when passengers rushed to one side as a rescue craft approached, authorities said. That incident spurred a bolstered European commitment to patrol the sea between Libya and southern Italy.
Various accounts put the site of Wednesday's wreck 15 to 75 miles north of Tripoli, the Libyan capital.
Lawlessness has reigned in the North African nation since strongman Moammar Kadafi was ousted in a 2011 rebellion backed by air power from the United States and its NATO allies. Largely undeterred by authorities, Libyan smugglers run a profitable network that moves migrants from deep in Africa to European cities and towns.
Europe has been enduring a migrant crisis on several fronts this summer.
While multitudes continue to risk the Mediterranean crossing, tens of thousands of others, many of them Syrians and Afghans, have been arriving on Greek islands in flimsy craft from Turkey. And in the French port of Calais, hundreds of migrants daily have been trying to sneak into the tunnel connecting France to Britain, despite French and British efforts to deter them.
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