The Greek coastguard have rescued 242 refugees when their wooden boat sank north of the island of Lesbos, but at least three drowned, including two small boys, authorities have said.
Two boys and a man were found drowned on Wednesday, and an extensive search was under way in the area.
Coastguards and local residents assisted the migrants off the vessel after it arrived at the port of Molivos on Lesbos.
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Medics provided first aid to small children who were lying on the ground wrapped in thermal blankets. Other migrants were given oxygen masks and rushed to the hospital in ambulances.
Lesbos, which lies less than 10km from the Turkish coast in the north Aegean Sea, has been a primary gateway for thousands of migrants entering the European Union's outermost border.
More than 500,000 refugees have entered Greece through its outlying islands this year, in what has become the biggest humanitarian crisis on the continent in decades.
Inflows have increased recently as refugees are trying to beat the onset of winter, crossing the narrow sea passages between Turkey and Greece on overcrowded small boats.
At a summit last Sunday, EU leaders agreed to cooperate further in handling the crisis, and to provide United Nations-aided housing for 100,000 people, half of them in Greece.
Aid organisations say it barely addresses the problem of ensuring safe and legal routes for people to seek refuge.