At least 39 migrants, including several children, have drowned trying to cross the Aegean Sea from Turkey to Greece, coastguards say.
More than 60 have been rescued from the sea near the Turkish resort of Ayvacik.
Local officials said they expected the death toll to rise when the capsized boat was searched.
Thousands of refugees and migrants continue to make the dangerous sea journey from Turkey to Greece to seek asylum in northern Europe.
The International Organization for Migration (IOM) said on Friday that 244 migrants had drowned in the Mediterranean so far this year, out of 55,568 arrivals.
"The daily average (of arrivals) is nearly equivalent to the total numbers for the month of January as recently as two years ago," the IOM said.
The latest tragedy comes just days after 26 migrants drowned when their boat sank off the coast of the Greek island of Samos.
The Turkish coastguard said that in Saturday's incident the migrants had been trying to reach the Greek island of Lesbos when their boat capsized.