The 88-metre commercial vessel Burcin had just left the Turkish port of Mersin when it was raided late Sunday night by coastguard personnel following a tip-off that there were migrants aboard.
Authorities say 333 migrants, most of them Syrian nationals, were taken into custody on Monday in an operation that involved hundreds of coastguard officers.
Turkey’s semi-official news agency Anadolu reported that four Turks and 11 Syrians suspected of human trafficking have been detained.
The Mediterranean city of Mersin has in recent months become a key hub for Syrian migrants seeking to enter the European Union.
Local media says the traffickers had transferred the migrants to the Burcin from smaller vessels, one of which tried to flee and was later caught by the coastguard.
Authorities in Mersin say that more than 1,750 illegal migrants were detained at sea off the port in the last year alone.