Rescuers pulled 24 bodies from the sea at the mouth of Istanbul's Bosphorus strait on Monday and rescued seven people after the sinking of a boat carrying migrants including children, the Turkish Coastguard Command said.
Tens of thousands of migrants from Africa, the Middle East and beyond pack into often unsafe boats each year and thousands of them drown in their efforts to enter the European Union through coastal states.
The boat, which capsized, was loaded with 42 Afghan illegal migrants, including 12 children and seven women, along with a Turkish captain, the Hurriyet news website reported. It was believed to have been heading for Bulgaria or Romania, but it was unclear where it set to sea.
Seven coastguard vessels and a helicopter were continuing search operations in the Black Sea, some 3 miles (5 km) north of the Bosphorus, the coastguard said in a statement.
Most of the migration to Europe happens via the Mediterranean Sea and the International Organisation for Migration (IOM) said last week that an estimated 3,200 migrants had died attempting to cross the Mediterranean this year.
"Many of them (are) victims of ruthless criminal gangs seeking to profit from the misery of men, women and children fleeing conflict and oppression," the IOM said in a statement on its website.