At least 24 people have been killed and scores are missing after a boat said to be carrying migrants sank off the north coast of Istanbul, reports GHN based on BBC.
The accident took place where the Bosphorus meets the Black Sea.
A large air and sea rescue operation is now under way.
The nationality of the migrants is not clear. Media reports say that it is unusual for a vessel carrying migrants to be in this area.
One theory is that the refugees were trying to get to Romania - a member of the European Union.
Two months ago another group of migrants - mostly Syrians and Afghans - was rescued by the Turkish coastguard off the northern coast of Istanbul reportedly heading for the EU.
"The wind is making our task very difficult. The boat is a very small one... But they were carrying 40 people in it. We are seeing bodies of children floating in the sea," rescuer Ali Saruhan was quoted by Hurriyet Daily News as saying.
Seven coastguard vessels and a helicopter are conducting the search in the Black Sea, some 5km (3 miles) north of the Bosphorus, the coastguard said in a statement.
Hurriyet says that since the beginning of the civil war in Syria, thousands of migrants have been trying to reach the EU by making the treacherous sea journey from the western and southern Turkish coast.
Tens of thousands of migrants have also attempted to cross the Greek and Bulgarian borders by land, the paper says.