At least 300 people who tried to cross the Mediterranean are missing, survivors of the crossing and the Italian Coast Guard tell the U.N. refugee agency.

They were among migrants and refugees mainly from sub-Saharan Africa who had sailed on four dinghies from the Libyan coast without food or water.

"This is a tragedy on an enormous scale and a stark reminder that more lives could be lost if those seeking safety are left at the mercy of the sea," Vincent Cochetel, the Europe bureau director for the U.N. High Commissioner for Refugees, said in a statement. "Saving lives should be our top priority. Europe cannot afford to do too little too late."

The UNHCR statement said some 29 people died Sunday on one dinghy. Some of them died of hypothermia, the Italian Coast Guard said. About 80 survivors landed in Lampedusa, off the Sicilian coast, after being rescued by the coast guard and a merchant vessel.

The Associated Press adds: "The nationalities of the survivors and those missing were not immediately given, but a large proportion of those arriving at the moment are fleeing conflicts in Iraq, Syria, Mali and elsewhere."

UNHCR and human rights groups have sharply criticized the EU's rescue efforts in the Mediterranean. The EU effort, called Triton, patrols Europe's borders and is limited to a few miles off the continent's coast. The operation it replaced in November, Italy's Mare Nostrum, sailed close to Libya's coast.

NPR's Sylvia Poggioli tells our Newscast unit that Italy ended Mare Nostrum because of its high costs, some $12 million a month.

"Saving lives must be a priority for the European Union," the UNHCR statement said.

Sylvia reports that aid agencies say bigger ships like those used in Mare Nostrum would have safely rescued the migrants.

In 2013, more than 300 migrants drowned off Lampedusa.

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