Greek authorities have launched a search and rescue operation in the eastern Aegean after a sailboat carrying dozens of migrants sank between the small islands of Agathonisi and Farmakonisi, near the Turkish coast.

The Greek coast guard said six people were rescued by a Greek helicopter, and another 10 by the Turkish coast guard while between 17 and 21 people were missing after the boat sank Tuesday.

Those rescued by the Turkish crews said there had been between 33 and 37 people on board. It was not clear why the boat sank, or what the migrants' nationalities were.

Tens of thousands of migrants have made their way from the Turkish coast to Greek islands so far this year, hoping to make their way to more prosperous European Union countries.