Turks are voting in presidential and parliamentary elections that pose the biggest ballot box challenge to Recep Tayyip Erdogan and his Islamist-rooted AK Party since they swept to power more than a decade and a half ago.
The vote on Sunday will also usher in a powerful new executive presidency long sought by Erdogan and backed by a small majority of Turks in a 2017 referendum. Critics say it will further erode democracy in the NATO member state and entrench one-man rule.
A crowd of President Erdogan's supporters chanted his name as he emerged from a school after voting in Turkey's largest city Istanbul, shaking hands with people amid tight security.
"Turkey is staging a democratic revolution," he told reporters in the polling station. "With the presidential system, Turkey is seriously raising the bar, rising above the level of contemporary civilisations."
Erdogan, the most popular but also divisive leader in modern Turkish history, argues the new powers will better enable him to tackle the nation's economic problems - the lira has lost 20 per cent against the dollar this year - and deal with Kurdish rebels in southeast Turkey and in neighbouring Iraq and Syria.
But he reckoned without Muharrem Ince, the presidential candidate of the secularist Republican People's Party (CHP), whose feisty performance at campaign rallies has galvanised Turkey's long-demoralised and divided opposition.
Addressing a rally in Istanbul on Saturday attended by hundreds of thousands of people, Ince promised to reverse what he and opposition parties see as a swing towards authoritarian rule under Erdogan in the country of 81 million people.
"If Erdogan wins, your phones will continue to be listened to ... Fear will continue to reign ... If Ince wins, the courts will be independent," said Ince, adding he would lift Turkey's state of emergency within 48 hours of being elected.
Erdogan told reporters voter turnout appeared good.
"This stability must continue and that can happen with Erdogan so I voted for him," said janitor Mehmet Yildirim, 48, in Istanbul. "With Erdogan, we stand stronger against the West."
Opposition parties and NGOs have said they were deploying half a million monitors at ballot boxes to prevent fraud. They argue election law changes and fraud allegations in the 2017 referendum raise fears about the vote's fairness.
The leader of the main opposition CHP party, Kemal Kilicdaroglu, said after voting in Ankara that his party had received complaints of voting irregularities in the southeast.
Turkey has been under emergency rule - which restricts some freedoms and allows the government to bypass parliament with decrees - for nearly two years since an attempted coup in 2016.
