Turkey's top politicians made a final effort on Saturday to sway undecided voters in a frenetic end to a bitterly-contested campaign in the referendum on expanding President Recep Tayyip Erdogan's powers.
Campaigning ends at 3pm GMT but both the 'Yes' and 'No' camps were squeezing in a flurry of rallies as the clock ticked down to Sunday's landmark poll.
Analysts see the poll as a historic choice on the direction of the NATO member which will shape its future political system and determine relations with the West.
If passed, the new presidential system will implement the most radical political shake-up since the fall of the Ottoman Empire, dispensing with the office of the prime minister and centralising the entire executive bureaucracy under the presidency.
Erdogan in a late night interview with TRT state television confidently predicted victory, saying surveys showed a 'Yes' vote of 55-60 percent.
"On Sunday I think that could be a very clear outcome in favour of 'Yes'" he said.
Opinion polls have predicted drastically different outcomes and victories for both sides. But the ruling party and presidency are widely believed to conduct their own confidential polling.
'Last messages'
Erdogan, who has dominated the airwaves in recent weeks with multiple daily rallies and interviews, was due to give four more speeches in Istanbul.
"God willing, this nation will celebrate tomorrow evening," he said in the first of the rallies. "Tomorrow is very important, you will definitely go to ballot box and cast your vote," he told supporters.
The standard-bearer of the 'No' camp, Republican People's Party (CHP) leader Kemal Kilicdaroglu, warned at a meeting in the Ankara region that Turkey was deciding if "we want to continue with the democratic parliamentary system or one man rule".
Watch: Campaigning ahead of the election
He described the new system as "a bus with no brakes and whose destination is unknown."
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 two co-leaders of the second opposition party the pro-Kurdish Peoples' Democratic Party (HDP), Figen Yuksekdag and Selahattin Demirtas, have been jailed on charges of backing Kurdish militants in what supporters say was a deliberate move to eliminate them from the campaign.
The HDP was due later Saturday to hold a final mass rally in its stronghold of Diyarbakir in southeast Turkey.
"The last messages," headlined the Hurriyet daily. "With one day remaining to the historic referendum the leaders are making the final calls to influence undecided voters."
Security an issue
The campaign, however, has not been plain sailing for Erdogan, and some heavyweight figures within the ruling Justice and Development Party (AKP) have been conspicuously silent on the new system.
Former prime minister Ahmet Davutoglu spoke before Erdogan at a 'Yes' rally in the Anatolian city of Konya on Friday but, to the amusement of opposition commentators, failed once to endorse the presidential system.
Watch: Turkey, voices of protest
The 'Yes' campaign also hit a last minute hitch when the Nationalist Movement Party (MHP), the AKP's partner in promoting the changes, reacted angrily to comments by a presidential adviser suggesting a federal system could be imposed in Turkey.
Such a system is an anathema to nationalists who believe in the indivisible unity of Turkey and particularly fear the creation of any Kurdish region in the southeast.
Erdogan moved rapidly to say that no such plan was on the agenda and MHP leader Devlet Bahceli said the issue was now closed.
Turkish media said all AKP advisers and ministers had been told to cancel TV interviews scheduled for the last hours of the campaign to prevent further slip-ups.
After a slew of attacks over the last year blamed on Kurdish militants and jihadists, security is set to be a major issue on polling day.
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.
More than 33,500 police officers will be on duty in Istanbul alone on referendum day, according to Turkish media.
