A dinghy overcrowded by migrants and refugees approaches the Greek island of Lesbos after crossing a part of the Aegean Sea from the Turkish coast September 20, 2015. [Photo/Agencies]

ATHENS/ANKARA - Thirteen migrants, including six children, died when their boat was wrecked in Turkish waters, a Turkish coastguard source said on Sunday.

It was believed to be the same incident as one reported by Greek authorities early on Sunday, in which an inflatable carrying 46 people towards the Greek island of Lesbos collided with a cargo vessel and capsized.

Six of those killed were children and 20 people were rescued, the Turkish source said. The search continues for 13 people missing. Seven of those rescued were receiving treatment.

Their nationalities were not immediately known.

"They (the migrants) told rescuers there were 46 people in the inflatable dinghy in total," a Greek coastguard spokeswoman said.

Rescues and sinkings occur almost daily in the often choppy seas off Greece's eastern islands.

Tens of thousands of mainly Syrian refugees have braved the short crossing from Turkey this year, mainly in flimsy and overcrowded inflatable boats.

A girl believed to be aged five died on Saturday and 13 others were feared drowned after their boat sank off Lesbos, a favoured entry point on a route that takes the migrants through the Balkans towards northern Europe.

Fifteen children were among 34 who died a week ago when their boat capsized off the small island of Farmakonisi.