At least 11 refugees, including five children, drowned and about 10 were missing after their boat sank overnight off the Greek island of Farmakonisi, Greek maritime police said Wednesday.Twenty-six people were saved and a search was under way in the southeastern Aegean Sea for other survivors from the capsized wooden boat.A Greek army helicopter was pressed into service with a vessel from the European Union's border agency Frontex to aid the search, they said.The dead also included two women and four men.Witnesses said the boat had sunk despite a calm sea and feeble winds.On Tuesday, at least six children died when a boat carrying Afghan migrants sank in Turkish waters while on its way to Greece.The Turkish coastguard recovered the bodies of the children, including a baby, and were still looking for two other migrants reported missing, the official Anatolia news agency said.The inflatable dinghy sank in strong winds and high waves near the town of Cesme in western İzmir province, Anadolu Agency said. It was apparently heading for the Greek island of Chios.More than 886,000 migrants have arrived in Europe by sea so far this year, according to the latest UN figures.Of them more than 650,000 -- for the most part refugees from war-torn Syria -- have undertaken a sea journey from Turkey to Greece to enter the European Union.