The Geneva-based United Nations refugee agency, UNHCR, confirmed on Friday that two boats carrying a total of 500 refugees had sunk off the Libyan port town of Zuwara.
"We are hearing media reports that there are about 100 survivors," UNHCR spokeswoman Melissa Fleming told journalists. "Our office in Libya is checking with the coastguard…We believe 200 are still missing, feared dead."
The Libyan Red Crescent's volunteers were meanwhile collecting bodies that had washed ashore.
"Until now 76 bodies have been retrieved from the sea and 198 people have been rescued," Mohammed Al-Misrati, who works with the organization, told reporters. "There are still people missing, but we don't know how many," he added.
The Malta-based group Migrant Report said many young children, between 1 and 3 years old were among the dead. Refugees from Syria, Bangladesh and African nations were among the victims.
The first boat, carrying around 50 people, signaled for help on Thursday. Around 400 passengers were traveling in the second vessel, which sank later. The Italian Coastguard, which coordinates refugee rescue missions in the Mediterranean, said it received no distress call.
The head of Libya's Red Crescent in Zuwara, Hussein Asheini, said some people died after being trapped inside one of the boats. Fishermen and the coast guard found the waterlogged vessel and towed it back to Zuwara.
"The boat sank out at sea and a coast guard team is still diving in and checking inside to see if there is anyone else," Asheini told reporters.
Many refugees fleeing conflict in the Middle East and Africa come to Libya to cross over the Mediterranean and reach Europe's shores. Human traffickers have taken advantage of the situation, charging huge sums for loading the migrants onto flimsy boats and taking them to Italy or Greece.
More than 2,500 people have died trying to reach Europe this year.
mg/jm (dpa, AFP, AP)