Voters across Turkey headed peacefully to the polls on Sunday to decide on the referendum on constitutional changes.

Residents in Istanbul, yeasayers and naysayers alike, have been casting their votes peacefully and smoothly amid tight security.

Thus far no incidents have been reported in Istanbul, with its almost one fifth of all the country's voters and the city which holds the key to the result.

If the "Yes" camp wins, Turkey will switch to an executive presidency from the parliamentarian system in place ever since the republic was founded in 1923.

"This referendum is not an ordinary voting," President Recep Tayyip Erdogan told journalists after casting his vote in the Asian side of Istanbul.

"We had plenty of elections concerning the parliamentary system in the republic's history, and we had several referendums, however this particular one is to decide whether to change the governance system."

If the 18-article constitutional amendments passes in the plebiscite, the president will be granted sweeping powers with less checks and balances, a scenario feared by the naysayers.

"People should think twice about what they really want," Nursen Tuzun, a worker at a polling station inside a school in central Istanbul, told Xinhua.

"This is a system change and it is very different from past elections, he said.

Residents of Istanbul who came to the polls to cast their votes were optimistic regarding the country's future though declined to reveal their choices.

"I hope the referendum will be auspicious for the country," a young voter named Zeynep Kirci told Xinhua while waiting in line to vote.

"We have to remain hopeful as this is our country," he added.

"We have endless hope for this country," Mehmet Sarpbakan, another voter, remarked.

In Istanbul, senior and frail voters managed to cast their votes with the help of family members, wheelchairs and crutches.

As the voting process has gone well in other parts of the country with police officers present at each polling station, on the other hand, a total of three people were reportedly killed in the southeastern city of Diyarbakir.

The three deaths occurred during a gunfire exchange between two groups who resorted to violence following disputes over conflicting political views at a polling station, reported the private Dogan News Agency.

Initial referendum results are expected in the evening.

 Source: Xinhua