The ‘Yes’ campaign had won 55.5 percent of the vote while the ‘No’ campaign had mustered 44.5 percent, the election commission said in figures quoted by state news agency Anadolu, in an initial count based on 65 percent of the ballot boxes.

The result could still change as more ballot boxes are counted across the hugely diverse country. The ‘No’ share of the vote was climbing as more ballots were counted, after lagging well behind in the early count, in a nail-biting end to the campaign.

For the changes to be implemented, the ‘Yes’ camp needs to win 50 percent plus one vote.

More than 55.3 million Turks were eligible to cast ballots on sweeping changes to the president’s role which, if approved, would grant Erdogan more power than any leader since modern Turkey’s founder Mustafa Kemal Ataturk and his successor Ismet Inonu.

Voting in Istanbul with his family, Erdogan predicted that “our people would walk to the future” by making the right choice.

After a stamina-busting campaign that saw insults flung in both directions, Prime Minister Binali Yildirim said: “Whatever choice comes out on top, our nation will make the most beautiful decision.”

Yildirim was later due to address supporters from the headquarters of the Justice and Development Party (AKP) in Ankara while Erdogan was due to watch the results in Istanbul.

Initial patterns showed that the Aegean and Mediterranean coastal regions and Kurdish-dominated southeast had backed the ‘No’ camp.

But the ‘Yes’ vote had held up in Erdogan’s Anatolian heartland and — crucially — was ahead in Turkey’s biggest cities of Istanbul and Ankara.

‘Vote for destiny’

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 people arrested in an unprecedented crackdown after the failed putsch of July last year.

“We are voting for Turkey’s destiny,” said the standard-bearer of the ‘No’ camp, Republican People’s Party (CHP) leader Kemal Kilicdaroglu.

The co-leaders of Turkey’s second largest opposition party, the pro-Kurdish Peoples Democratic Party (HDP) Selahattin Demirtas and Figen Yuksekdag, have been jailed on charges of links to Kurdish militants in what the party says is a deliberate move to eliminate them from the campaign.

Closely watched on Monday will be the initial assessment of the international observer mission of the OSCE Office for Democratic Institutions and Human Rights (ODIHR) and the Parliamentary Assembly of the Council of Europe (PACE).

Three people were killed in a shootout in the garden of a school used as a polling station in the southeastern Diyarbakir region, the Dogan news agency said, but it was not clear if the fighting was linked to the election or simply a family feud.

If passed, the new presidential system would dispense with the office of prime minister and centralise the entire executive bureaucracy under the president, giving Erdogan the direct power to appoint ministers.

The system would come into force after the elections in November 2019. Erdogan, who became president in 2014 after serving as premier from 2003, could then seek two more five-year terms.

Supporters see the new system as an essential modernisation step for Turkey that will remove the risk of the political chaos that blighted the 1990s and is blamed for the 2000-2001 financial crisis.

Opponents fear it risks granting Erdogan authoritarian powers and allow him to ride roughshod over key institutions like the judiciary and parliament.

In the Kurdish-majority southeastern province of Diyarbakir, self-employed Nihat Aslanbay said he voted against the reforms.

“A one man regime will not bring any benefits to this country,” he said.

But in Istanbul, voter Emrah Yerlinkaya said he voted ‘Yes’ “to support” Erdogan. “If we are here today, it is thanks to him. I also voted because I support the constitutional reform.”

‘Drastic shake-up’

Beyond changing the government system, the vote could also have even wider implications for Turkey which joined NATO in 1952 and 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”.