The boat was carrying 45 people. (Representational)
A migrant boat carrying 45 people sank off southwest Turkey and the coast guard was scouring the sea for survivors, the Turkish defence ministry said Friday.
The coast guard was searching for the missing boat "after receiving a tip-off" that it sank on Thursday some 260 kilometres (160 miles) off the coast of the holiday resort town of Kas, the ministry said in a statement.
There was no immediate information on the nationalities of the migrants.
Illegal immigrants often use Turkey as a gateway to reach prosperous European Union states, mainly via Greece.
Many rely on smugglers and risk their lives through perilous journeys in overcrowded boats.
In 2016, Turkey inked a deal with the EU to stem the flow of migrants to Europe in return for some incentives including financial assistance.
Turkey currently hosts some 3.7 million refugees from the conflict in Syria and has been used by the EU as a bulwark to help stem the flow of migrants into Europe.
President Recep Tayyip Erdogan has long demanded more assistance from the EU to deal with the refugees and has previously threatened to open Turkey's border if the bloc does not provide additional funds.
In June, EU leaders gave a greenlight to plans to give Turkey another 3 billion euros ($3.6 billion) over the next few years to provide fresh assistance to Syrian refugees on its territory and to help the country boost border controls.
The plan for the new funding is part of a range of enticements that the bloc is using to try to keep Erdogan on side, with Brussels also offering to modernise a customs union with Turkey and start high-level talks on issues from health to security.
But Turkey has called reducing cooperation on migration to a financial dimension "a big delusion" while urging greater cooperation with the EU to tackle the issue.
Ankara has repeatedly said it wants a review of the 2016 deal in a fashion that "responds to the needs of the day and common interests".
Turkey now fears a fresh wave of Afghan refugees as US troops withdraw following 20 years of fighting against the Taliban, which has been regaining territory recently.
Erdogan this week said Turkey was holding talks with the Afghan authorities over the issue of migrants.