The Turkish referendum registered its negative when two people were killed in a gunfight during the voting exercise.
The incident happened in a village schoolyard which is being used as a polling station in the southeastern province of Diyarbakir.
The clash occurred in the district of Cermik, around 90 km northwest of the city. The cause of the clash is still unclear.
Security has been tight in predominantly Kurdish area of the country as Turkey votes on changing the constitution that will give President Tayyip Erdogan new sweeping powers.