Amir Cicek, governor of Mugla province, said the 8-meter boat which set off from the coastal village of Gumusluk sank early Sunday off the Turkish coast.
The area is part of the larger Bodrum peninsula, a popular tourist destination where this summer the body of drowned toddler Aylan Kurdi washed up, sparking international outrage.
While Kos is just 4 km (2.5 miles) from Bodrum at its closest, the journey is perilous, as migrants often cram into rubber dinghies captained by men with little or no seafaring experience.
The boat was carrying 37 people, 20 of whom were rescued, when it sank in the Aegean Sea according to the official, according to Turkey-based Anadolu Agency.
On Saturday night, the Turkish Coast Guard intercepted two boats carrying 31 Syrian and Afghan refugees heading to Kos, which is around 5 kilometers (3 miles) from Turkey. Ten Syrians were pulled from the sea as they tried to swim back to Turkey.
Two weeks ago, 15 refugees drowned in Bodrum’s bay when their boat sank.
A record 300,000 or more Syrians and other migrants have arrived in Greece, mostly setting off from Turkey's Aegean coast, according to the International Organization for Migration.