Eight migrants including children have drowned near the Aegean city of Izmir, the Turkish coast guard said.
Twelve other people are missing but 21 have been rescued.
According to the Turkish DHA news agency, six children were among the dead.
In a separate incident late on Wednesday, the agency reported that coast guards caught two suspected smugglers and rounded up 45 Syrian would-be migrants heading from Mugla province in south-west Turkey to the Greek island of Symi.
Earlier this week, the Geneva-based International Organisation for Migrants said more than one million asylum-seekers have entered Europe during 2015, almost all arriving by sea. It said 3,692 people have drowned trying to get into Europe.