Turkey's President Recep Tayyip Erdogan has claimed victory in a referendum granting him sweeping new powers, hailing the result as an "historic decision".
Turkey's two main opposition parties said they would challenge the results over alleged violations.
Turkey's three largest cities - Istanbul, Ankara and Izmir - all voted "No" although "Yes" prevailed in Erdogan's Anatolian heartland.
According to the preliminary results of the Turkish referendum, as many as 51.3% of voters supported constitutional amendments replacing the country's parliamentary system with an all-powerful presidency and eliminating the position of prime minister.
Erdogan declared that Turkey's had made a "historic" decision and appeared standing on top of a bus in front of thousands of cheering supporters outside his Huber Palace Istanbul residence on the shores of the Bosphorus. "That is why it is very significant", Erdogan added.
Under the changes, most of which will only come into effect after the next elections due in 2019, Turkey's governance will be transformed from a parliamentary system to an executive presidency.
The president survived a coup attempt previous year and responded with a crackdown, jailing 47,000 people and sacking or suspending more than 120,000 from government jobs such as schoolteachers, soldiers, police, judges or other professionals.
The High Electoral Board initially said it would not accept ballots that were missing ballot commission stamps, but changed course after voting was underway, saying it would accept unstamped ballots "unless they are proven to have been brought from outside".
Meanwhile Turkey was set to extend a almost nine-month state of emergency, CNN Turk and NTV television reported.
Western reactions to the referendum will be crucial after Erdogan accused Turkey s allies of failing to show sufficient solidarity in the wake of the failed coup.
Speaking to Al Jazeera, Bulent Aliriza, director of the Turkey Project at the Center for Strategic and International Studies, said the outcome of the referendum confirmed Erdogan's dominance in the country's politics but also exposed divisions within Turkish society.
The party has said it will contest the result of the referendum. "The outcome of the vote is a clear signal against the EU", Kurz, who also now chairs the OSCE, said in a statement for the APA agency.
This referendum was controversial by which the Turkish opposition - represented in the Republican People's Party and the Peoples' Democratic Party - rejected the batch of amendments composed of 18 items while the Nationalist Movement Party approved it.
During the campaign, Erdogan repeatedly attacked European countries, including Germany and the Netherlands, accusing them of "Nazi-like" tactics for banning his ministers from speaking to rallies of Turkish voters overseas.
"Our citizens overseas are also a significant part of this victory", Erdogan said.
As a result of the referendum result, the president will have a maximum of two five-year terms and can directly appoint ministers and several vice-presidents.
The president will become the head of the executive branch and will be allowed to issue decrees, including the right to declare a state of emergency.