Turks were voting Sunday in dual parliamentary and presidential polls seen as President Recep Tayyip Erdogan's toughest election test, with the opposition revitalised and his popularity at risk from growing economic troubles.
Erdogan has overseen historic change in Turkey since his Islamic-rooted ruling party first came to power in 2002 after years of secular domination. But critics accuse the Turkish strongman, 64, of trampling on civil liberties and displaying autocratic behaviour.
With all eyes on the transparency of the vote, polling stations opened at 0500 GMT and were due to close at 1400 GMT, with the first results expected late in the evening.
Over 56 million eligible voters are for the first time casting ballots simultaneously in the parliamentary and presidential elections, with Erdogan looking for a first round knockout and an overall majority for his ruling Justice and Development Party (AKP).
But both these goals are in doubt in the face of an energetic campaign by his rival from the secular Republican People's Party (CHP), Muharrem Ince, who has mobilised hundreds of thousands in mega rallies, and a strong opposition alliance in the legislative polls.
"I hope for the best for our nation," said Ince as he cast his ballot in his native port town of Yalova south of Istanbul, vowing to spend the night at the headquarters of Turkey's election authority in Ankara to ensure a fair count.
Erdogan remains the favourite to hold on to the presidency -- even if he needs a second round on July 8 -- but the outcome is likely to be much tighter than he expected when calling the snap polls one-and-a-half years ahead of schedule.
Analysts say the opposition's performance is all the more troubling for the authorities given how the campaign has been slanted in favour of Erdogan, who has dominated media airtime.
"Even if the odds are on the incumbent's side, the race is likely to be far tighter than many expected," said Ilke Toygur, analyst at the Elcano Royal Institute and adjunct professor at University Carlos III in Madrid.
Anthony Skinner, head of MENA at Verisk Maplecroft, added: "Ince's wit, audacity, ability to poke holes through Erdogan's narrative and connect with Turks beyond the traditional base of his secularist CHP has flustered Erdogan and his team."
The stakes in this election are particularly high as the new president will be the first to enjoy enhanced powers under a new constitution agreed in an April 2017 referendum strongly backed by Erdogan.
The president had for the last two years ruled under a state of emergency imposed in the wake of the 2016 failed coup, with tens of thousands arrested in an unprecedented crackdown which cranked up tensions with the West.
Erdogan, whose mastery of political rhetoric is acknowledged even by critics, has won a dozen elections but is now fighting against the backdrop of increasing economic woes.
Inflation has zoomed well into double digits -- with popular concern over sharp rises in staples like potatoes and onions -- while the Turkish lira has lost some 25 percent in value against the US dollar this year.
"At each election, I come with hope. But this year I have a lot more faith, but we'll see," said voter Hulya Ozdemiral as she cast her ballot in Istanbul
The votes of Turkey's Kurdish minority will be especially crucial in the parliamentary poll. If the pro-Kurdish Peoples' Democratic Party (HDP) wins seats by polling over the 10 percent minimum threshold, the AKP will struggle to keep its overall majority.
But in a situation labelled as blatant unfairness by activists, the HDP's presidential candidate Selahattin Demirtas has campaigned from a prison cell after his November 2016 arrest on charges of links to outlawed Kurdish militants.
After casting his ballot in his jail in the northwestern region of Edirne, Demirtas wrote on Twitter: "I wish that everyone uses their vote for the sake of the future and democracy of the country."
The opposition has also alleged heavy bias in favour of Erdogan by state media, with news channel TRT Haber not showing a single second of Ince's giant final Istanbul rally live.
Voting already closed last week for Turkish citizens resident abroad, with just under 1.5 million out of just over 3 million registered voters casting their ballot, a turnout of just under 49 percent.
Tens of thousands of Turkish citizens are responding to calls from the opposition to monitor the polls for a clean election and a delegation of observers from the OSCE will also be in place.
High security is in place across the country, with 38,480 police officers on duty in Istanbul alone. As is customary in Turkey on polling days, sales of alcohol in shops are also prohibited.