A boat carrying suspected migrants from Afghanistan and Syria sank today off Istanbul's coast, leaving at least 22 people dead.
About a dozen people were believed to be missing while six were rescued.
Coast guard vessels, divers and passing fishing boats were scanning the waters just north of the Bosphorus Strait for more survivors.
There were about 40 people on board the boat, the coast guard said. It was unclear what caused the vessel to sink or where it had set sail from.
The coast guard revised earlier figures of 24 dead and seven rescued.
The people on board were believed to be from Afghanistan and Syria, said Colonel Sakir Cicek, of the Turkish military's general staff command in the capital Ankara.
Emrecan Kolcu, one of the fishermen involved in the search and rescue operation, said he headed to the area when another fisherman radioed that he had seen a body in the sea.
"We saw dead bodies," Mr Kolcu said. "It was not possible not to see them anyway. Everywhere was full of dead bodies. They had life vests on them."
The boat had issued a distress call early today about three miles north of the Bosphorus Strait in the Black Sea, authorities said.