Turkish voters are going to the polls to decide whether to grant President Recep Tayyip Erdogan a second five-year term, in the country's most fiercely-fought elections in years.
If he wins another term, Mr Erdogan plans to scrap the post of Prime Minister, a measure opponents say will erode democracy.
But he faces a major challenge from centre-left candidate Muharrem Ince of the Republican People's Party (CHP).
Turkey remains under a state of emergency imposed in the aftermath of a failed coup in July 2016.
These elections were originally scheduled for November 2019 but were brought forward by Mr Erdogan.
Mr Erdogan and his main rival Muharrem Ince both held huge rallies on Saturday, their final day of campaigning - and each branded the other unfit to run Turkey.
Mr Ince, whose fiery campaigning has revitalised Turkey's demoralised opposition, promised to push back what he characterised as a slide into authoritarian rule under Mr Erdogan.
"If Erdogan wins, your phones will continue to be listened to... Fear will continue to reign," he told at least a million people gathered in Istanbul. "If Ince wins, the courts will be independent."
Mr Ince also said that if elected, he would lift Turkey's state of emergency within 48 hours. Emergency rule allows the government to bypass parliament.
At his own rally, President Erdogan - who was prime minister for 11 years before becoming president in 2014 - used a violent metaphor to summarise his hoped-for result, asking supporters, "Are we going to give them an Ottoman slap [a technique for knocking someone out] tomorrow?"
He accused Mr Ince - a former teacher and MP of 16 years - of lacking the skills to lead.
"It's one thing to be a physics teacher, it's another thing to run a country," Mr Erdogan said. "Being president needs experience."
He told supporters he planned to push through more major infrastructure projects to boost the economy.
How will the voting work?
Two votes are being held on Sunday - one to choose Turkey's next president, and another to pick members of parliament.
Around 60 million Turks are eligible to take part.
Six candidates are vying for the presidency, and if one of them wins more than 50% of the vote they will be elected outright.
If nobody hits that threshold, the top two will face off in a second-round vote on 8 July.
Mr Erdogan will be hoping to win decisively, as a run-off vote could end in defeat or narrow his margin of victory.
In the parliamentary election, the president's AK Party (AKP) will face a tough battle to keep its majority in the 600-seat assembly.
The contest pits a government-led coalition against an alliance of opposition parties.
The performance of the pro-Kurdish Peoples Democratic Party (HDP) could prove decisive. If it hits the 10% vote-share needed to enter parliament, it will be harder for the AKP to retain its dominance.
The HDP's presidential candidate Selahattin Demirtas is presently detained in a high-security prison on terror charges, which he firmly denies.