Millions of Turks will head to the polls on Sunday to vote in a tight referendum race that could transform the country into a presidential republic, granting sweeping new powers to the President.

President Recep Tayyip Erdogan is seeking to replace the parliamentary system with an executive presidency, Hürriyet Daily News reported.

Approval could see him stay in office until 2029.

About 55 million Turkish voters will be casting votes following a divisive campaign in October 2016 when the Nationalist Movement Party (MHP) announced its support to the ruling Justice and Development Party's (AKP) project of replacing the current government system with a presidential system.

The Supreme Board of Election announced that 167,140 ballot boxes will be ready for voters. The election process for Turkish citizens living abroad ended on April 9. Over a million registered citizens voted at 120 foreign missions in 57 countries.

Polls open at 7 00 a.m. (local time) and close at 4-00 p.m. on Sunday in 32 eastern provinces, and open and close an hour later in the rest of the country, said the report.

Supporters say a "yes" vote would streamline and modernise the country whereas opposition "no" camp fear the move would lead to increasingly authoritarian rule.

The "yes" campaign supported by Erdogan, Prime Minister Binali Yildirim and the ruling AKP has dominated Turkey, while the opposition "no" camp had faced threats, violence, arbitrary detentions, a lack of TV airtime, and disregard by pro-government media.

Critics fear the change would put too much power in the President's grasp, amounting to one-man rule, without the checks and balances of other presidential systems.

The referendum could bring about the biggest change to the governing system since the modern republic was founded almost a century ago.

It also takes place under a state of emergency which was imposed following a failed coup last July.

President Erdogan was holding his final rally in Istanbul and said he was confident of victory.

The referendum on constitutional change would abolish the post of Prime Minister, allowing the President to appoint cabinet ministers and bring all state bureaucracy under his control.

If the package is approved, the President will be able to retain ties with the political party he or she belongs to.

The changes will also grant authority to the President to issue decrees within the executive jurisdiction, declare a state of emergency and appoint public officials.

The President will also be able to declare a state of emergency without necessary cabinet approval and to draft the budget, which is currently drawn up by Parliament.

The changes will allow the President to dissolve Parliament.

Erdogan said the new system will bring stability in a time of turmoil marked by a Kurdish insurgency, Islamist militancy and conflict in neighbouring Syria.

The referendum has a simple "yes" or "no" choice on whether to endorse Parliament's approval of a new draft Constitution.

Results of the elections are expected late on Sunday evening.