(CNN) At least 170 people are feared dead after they went missing from two separate shipwrecks on the Mediterranean Sea that left from Libya and Morocco, the United Nations said.

"Some 53 people have died on the Alborán Sea, western Mediterranean, according to recent information from NGO sources," the UN High Commissioner for Refugees (UNHCR) said in a statement on Saturday.

"One survivor is understood to have been rescued by a passing fishing boat after being stranded for more than 24 hours at sea and is receiving medical treatment in Morocco."

UNHCR added that rescue vessels from Moroccan and Spanish rescue searched for the boat and survivors "for several days to no avail."

Meanwhile, the non-governmental organization Sea Watch said in a statement Saturday night that there were only three survivors from a shipwreck in the central Mediterranean.

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