Five migrants were killed on Tuesday when their boat sank in the Aegean Sea while trying to cross from Turkey's western coast to EU member Greece, reports said.
Sixteen more people were rescued by air and by sea in a search and rescue operation by the Turkish coastguard, the Doğan news agency said.
The migrants had earlier set off from the Didim district in Aydın province in an apparent bid to reach the Greek island of Farmakonisi.
Turkey, which is home to at least 2.2 million refugees from Syria's civil war, has become a hub for migrants seeking to reach Europe, many of whom pay people smugglers thousands of dollars for the risky crossing.
Ankara reached an agreement with the EU in November to stem the flow of refugees heading to Europe, in return for 3 billion euros in financial assistance.
But the deal and the onset of winter do not appear to have deterred the migrants, with boats still arriving on the Greek islands daily.
According to a statement by the International Organisation for Migration (IOM) Tuesday, 45,361 migrants have arrived in Greece by sea so far this year, 31 times more than for all of January 2015.
Some 90 percent of the new arrivals are from Syria, Iraq and Afghanistan, it added.
The IOM said it has recorded 158 deaths in the eastern Mediterranean this year, along with 19 more in the central Mediterranean, bringing the total number of deaths in 2016 to 177.