Over 55.3 million Turks are able to vote in the referendum on sweeping changes to the president's role which, if agreed, would grant Erdogan more power than any leader of Turkey since its founder Mustafa Kemal Ataturk and his successor Ismet Inonu.
Opinion polls, always treated with caution in Turkey, predicted wildly divergent scenarios with analysts saying the outcome remains too close to call despite the clear advantage in resources and airtime enjoyed by the 'Yes' campaign.
But he urged people not to succumb to "lethargy" in voting, saying "the stronger result the better".
"A 'Yes' that emerges from the ballot box with the highest margin will be a lesson to the West," he said in the Istanbul district of Sariyer, the last of a stamina-busting sequence of rallies.
If passed, the new presidential system would dispense with the office of the prime minister and centralise the entire executive bureaucracy under the presidency, giving Erdogan the direct power to appoint ministers.
But it could also have even wider implications for the key NATO member, which for the last half century has set its sights on joining the European Union.
Erdogan has warned Brussels that in the event of a 'Yes' vote he would sign any bill agreed by parliament to reinstate capital punishment, a move that would automatically end its EU bid.
Western reactions to the referendum outcome will be crucial, after Erdogan accused Turkey's allies of failing to show sufficient solidarity in the wake of the July 15 failed coup.
Sinan Ekim and Kemal Kirisci of the Brookings Institution think-tank said in a report the changes if agreed "would set in motion the most drastic shake-up of the country's politics and system of governance in its 94-year-long history".
The opposition has cried foul that the referendum has been conducted on unfair terms, with 'Yes' posters ubiquitous on the streets and opposition voices squeezed from the media.
The poll is also taking place under a state of emergency that has seen 47,000 arrested in an unprecedented crackdown after the botched putsch.
The standard-bearer of the 'No' camp, Republican People's Party (CHP) leader Kemal Kilicdaroglu, warned at his final rally that Turkey was deciding if "we want to continue with the democratic parliamentary system or one-man rule".
He described the new system as "a bus with no brakes and whose destination is unknown".
Voting in the country's east gets under way at 7.00 AM and an hour later elsewhere.
Key factors influencing the result will include whether the ruling Justice and Development Party (AKP) can perform the delicate balancing act of bringing both nationalists and conservative Kurds behind the new system.
Authorities in Istanbul on Friday detained five people suspected of planning an attack on polling day, following the arrest of 19 alleged Islamist extremists in the Aegean city of Izmir earlier in the week.
The Dogan news agency said a total of 49 IS suspects had been detained in Istanbul alone over the last week.
More than 33,500 police officers will be on duty in Istanbul alone on referendum day, according to Turkish media.
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