Parliamentary elections were also held on Sunday, with Erdoğan's AK Party leading the vote with 42 percent, according to the official results.
Turkish President Recep Tayyip Erdogan is preparing to extend his rule and take on new powers after his victory in elections on Sunday.
State media also reported on Sunday that Erdogan's AK Party holds 43 percent, while the opposition party holds 23 percent of the vote, with 96 percent of the total vote counted.
Ince, of the secular Republican People's Party (CHP), conceded defeat in a news conference in Ankara, but railed against the vote, which he said was unfair and would have serious consequences for Turkey's democracy.
Polls closed at 5 p.m. local time, and though Turkey does not have exit polls, the Supreme Electoral Council said it hoped to announce preliminary results before midnight.
More than 56 million people were registered to vote at 180,000 ballot boxes across Turkey.
"I will keep up the fight as someone who got the approval of one person among every three in Turkey", he added. Erdogan will most likely try to capitalize on his new mandate and seek to extract concessions from the United States in Syria and prevent military sanctions from brewing in the U.S. Congress.
In a series of Twitter postings, Demirtas praised the party's success in winning a projected 67 seats out of 600, according to unofficial results.
The HDP's presidential candidate, Selahattin Demirtas, waged his election campaign from a prison near the Greek border as he awaits trial on terrorism-related charges, which he denies.
"The restrictions we have seen on fundamental freedoms have had an impact on these elections".
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The win allowed Erdogan to escape a run-off against his closest rival, Muharrem Ince, who posed the greatest threat to ending Erdogan's 15-year political dominance.
She was referring to Erdogan´s victory speech in which he said the nearly 90 percent voter turnout "taught the entire world a democracy lesson".
Under constitutional amendments approved after a controversial 2017 referendum, Turkey is making a transition from a parliamentary system to a presidential one.
Mr Erdogan has presided over a strong economy and built up a solid support base by investing in healthcare, education and infrastructure.
Under the new presidential system, the prime minister's position no longer exists and executive powers are given to the president, who rules with limited checks and balances.
The HDP passing the threshold is key for the opposition: Forecasts show that without them in parliament, the AKP and their junior coalition partner, the Nationalist Movement Party (MHP), would once again win the majority of seats. They will continue to "liberate Syrian lands", he said, so that the 3.5 million refugees now living in the country can one day go home.
"This is no longer a Turkey we want".
Erdogan has declared himself an "enemy of interest rates", raising fears he will pressure the central bank to cut borrowing costs after the election despite double-digit inflation. "The presidential election is certainly going to a second round".
As Turkey's democracy backslides, its European Union accession seems ever further away; however, Turkey will not want to lose European Union investment and trade and the West will not sacrifice the geostrategic importance of the country so relations, although perhaps strained, seem set to continue.
Ince told a rally on Saturday he would lift the state of emergency within 48 hours of being elected president.
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.