Six people were rescued and two are still missing from the stricken vessel, which had 15 people on board, the governor of Turkey's Mugla province Amir Cicek told the official Anatolia news agency.
He said the boat had gone down due to engine failure off the Mediterranean town of Marmaris as it tried to reach the Greek island of Kos.
The migrants were mainly Iraqi and Iranian nationals, Cicek added.
The Greek coast guard said it was helping Turkey with the rescue effort and had sent one helicopter and a patrol ship.
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Turkey, which is already sheltering 1.7 million refugees from the Syrian civil war, has become a key transit point for migrants seeking a better life in Europe.
Many pay people smugglers thousands of dollars to travel towards EU states in small boats, but the journey fraught with danger.
Thirty-seven migrants, believed mainly to be of Afghan origin, lost their lives in November when their overloaded boat sank in the Black Sea off Istanbul.
Smugglers in recent months have also been using large cargo ships to move illegal immigrants.