Although Erdogan is seen as the front-runner, he must secure more than 50 percent of the vote Sunday for an outright win.
Polls show Erdogan falling short of a first-round victory in the presidential race.
His main challenger, Muharrem Ince, also held a rally in Istanbul. Jailed candidate Selahattin Demirtas hovered at around 6%.
More than 56 million people were registered to vote at 180,000 ballot boxes across Turkey. Four representatives of the four parties represented in the current parliament are represented at these provincial stations, but they can only intervene in the final stage.
Erdogan faced an energetic campaign by the Ince, who has rivaled the incumbent's charisma and crowd-pulling on the campaign trail, and a strong opposition alliance in the legislative poll.
If he fails, he'll be forced into a July 8 runoff with the most successful opposition candidate, most likely Muharrem Ince of the secular Republican People's Party (CHP).More news: Hornets Players Were Reportedly ‘Sick And Tired’ Of Dwight Howard
The votes of Turkey's Kurdish minority will be especially crucial in the parliamentary poll.
"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.
"This is no longer a Turkey we want. Have no fear and don't believe in demoralizing reports", Ince said after polls closed.
Turkey's President and ruling Justice and Development Party, or AKP, leader Recep Tayyip Erdogan comes out of a voting booth to cast his ballot in Turkey's elections at a polling station in Istanbul, Sunday, June 24, 2018. But critics accuse the Turkish strongman of trampling on civil liberties and displaying autocratic behaviour.
According to Skynews, on Saturday, up to a million people turned out for one of the last opposition campaign rallies ahead of Sunday's elections.
These elections will complete Turkey's transition to a new executive presidential system, a move approved in a referendum in April 2017. Initiated by "Oy ve Ötesi" (Vote and Beyond) a few years ago, there are now dozens of such groups organizing tens and thousands of volunteers across the country - either to sign up as ballot observers from the lists of political parties or as independent observers, as permitted by Turkish election law.More news: The new Time magazine cover slams Donald Trump over family separation policy
As he runs Turkey under a state of emergency crackdown imposed after a failed coup in 2016, Mr. Erdogan has concentrated enormous powers in his hands. And the economy is struggling: The Turkish lira is down 20 percent this year and inflation is running at 18 percent.
"At each election, I come with hope".
Ballots of Turkey's presidential and parliamentary elections are being counted at a polling station in Diyarbakir, Turkey June 24, 2018.
Turkey has been under emergency rule - which restricts some freedoms and allows the government to bypass parliament with decrees - for almost two years since an attempted coup in 2016.
High security is in place across the country, with 38,480 police officers on duty in Istanbul alone.
The sale of alcoholic beverages is banned from 0300 GMT (6:00am) to 2100 GMT (00:00pm) while consumption of alcoholic beverages is also prohibited in public places.More news: Uruguay make their best start to a World Cup since 1954
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