As many as 700 people are feared dead after a fishing boat capsized in waters off Libya Saturday night in what could be the deadliest tragedy involving migrants being smuggled to Europe. Italy’s Coast Guard has rescued 49 survivors and about 20 bodies; as many as 700 are believed to still be in the water, the U.N.’s refugee agency—UNHCR—tells the Guardian. In a statement, the Coast Guard said it believed the 66-foot vessel overturned when migrants rushed to one side of the boat as they saw another vessel approach, reports the Associated Press. “They wanted to be rescued. They saw another ship. They were trying to make themselves known to it,” Barbara Moline, a UNHCR spokeswoman said.