It was not clear where the boat was headed or where it left from. Hundreds of thousands of refugees crossed the sea channel from Turkey to Greek territory in 2015 before Ankara curbed the flow under a deal it struck with the European Union.
The coast guard said the boat sank off the coast of Turkey's Izmir province after water began leaking shortly after its departure. Search and rescue operations for the missing refugees were continuing, a coast guard statement said. It said there were initially around 35 refugees on the boat in total, Presstv Reported.
Turkey became one of the main launch points for more than a million refugees taking the sea route to EU territory in 2015, many fleeing conflict and poverty in the Middle East and Africa.
The influx of refugees was drastically curtailed by a 2016 accord between Ankara and the EU, after hundreds died crossing to Greek islands a few miles off the Turkish shore.