Three more migrants survived for hours in the motorboat's overturned hull, breathing air trapped in a pocket, before being rescued by divers, the emergency worker said.
Those who drowned were attempting perhaps the safest, shortest sea crossing in the risky journey to Europe, for the Greek island of Kos is only four kilometers from Turkey at its closest point.
Turkish coast guards unloaded five body bags at the harbor in the western tourist town of Bodrum as the rescued migrants, one man clutching his head in his hands, sat on the wharf.
The Turkish divers pulled a child and two men out alive from a sealed area of the capsized boat, a 9-meter (30-foot) motorboat, the rescue official said. Medical staff carried a wailing young boy, an oxygen mask around his neck, and a man to ambulances.
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It wasn't the only rescue Tuesday in the Aegean Sea. About 20 other migrants were picked up by Turkish authorities and taken to the nearby town of Turgutreis. It was not clear what boat they had been on.
"It shows that there is a need to increase the capacities in the search and rescue operations here," Doctors Without Borders field coordinator Elisa Galli said.
Yet the numbers of migrants attempting perilous sea crossings to Europe continue to climb despite the risks.
As of Saturday, Italy said another 103,000 migrants have been rescued at sea and brought to Italy. Along with those landing in Spain and Malta, that means more than 243,000 migrants have reached Europe by sea so far this year, compared to 219,000 for all of 2014.