Turkish naval ships and an aircraft have been deployed as part of search and rescue efforts.
A boat carrying 45 migrants and refugees has sunk off southwest Turkey, prompting the coastguard to launch a search and rescue mission, the Turkish defence ministry said.
The ministry said in a statement on Friday it had received information on Thursday evening that the vessel was sinking, some 259km (161 miles) southwest of the Turkish resort town of Kas.
Turkish naval ships and an aircraft were on Friday carrying out search and rescue operations, the statement added.
It was not immediately clear whether any of the individuals on board had been rescued. There was also no immediate information on the nationalities of those involved.
Migrants and refugees often use Turkey as a gateway to reach the European Union, mainly via Greece.
Many rely on smugglers and risk their lives through perilous journeys in overcrowded boats.
In 2016, Turkey signed a deal with the EU aimed at curtailing migrant and refugee arrivals from the country into Europe in return for some incentives including financial assistance.
Turkey currently hosts some 3.7 million Syrian refugees.
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 green light to plans to give Turkey another three billion euros ($3.6bn) 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 bloc 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 migrants and refugees from Afghanistan after the United States withdrew its troops from the country following years of fighting against the Taliban armed group, which has been regaining territory recently.
Erdogan said this week that Ankara was holding talks with Afghan authorities over the issue of possible migrant and refugee arrivals.