According to Save the Children, Italy, a boat carrying 550 people capsized 24 hours after departing Libya.
The Italian coast guard had rescued 144 people, mostly sub-Saharan Africans, on Monday and launched an air and sea search operation in hopes of rescuing others, BBC reported.
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People who were rescued have been brought to a southern Italian port on Tuesday morning, Save the Children reported.
"Many of the victims are thought to be unaccompanied children," said Save the Children official.
Nine bodies have already been recovered, but no more survivors have been found since then.
Save the Children, Italy is still trying to find out how many young people were on the boat. "There were a few minors" among the survivors.
The migration season had just started, and "when the weather improves... we may have many more arrivals," said the official.
Late last year, the EU scaled back its maritime rescue operations, as some argued the service could encourage more migrants.