Turkey's Erdogan renews hold on power with election victory He's been in power for 15 years.

BEIRUT -- Turkish President Recep Tayyip Erdogan celebrated a sweeping re-election victory after a hard-fought campaign that proved to be his most challenging political battle after nearly 15 years in power.

Erdogan declared victory overnight, just a few hours after polls closed on Sunday evening.

"The winner of this election is each and every individual among my 81 million citizens," he said.

According to official results, Erdogan took 53 percent of the vote, with his ruling Justice and Development Party (AKP) also making gains. An extremely high voter turnout was recorded with nearly 87 percent of the electorate casting ballots.

Muharrem Ince, Turkey's main opposition candidate, conceded defeat but described the election as "unjust" and warned that Turkey was entering a dangerous regime of one-man rule.

Burcu, a 29-year-old shopkeeper in Istanbul who declined to provide his last name, told ABC News he voted for Ince and is suspicious of the official results.

"I am so disappointed," he said. "I would have said [Erdogan's party] cheated but I just watched Mr. Ince conceding the election and accepting the results without protest."

Critics complained about what they say were unequal campaign conditions with Erdogan dominating media coverage in a country that has been named the world's worst jailer of journalists.

With election victory in hand, Erdogan will rule with new muscle provided by sweeping changes to the constitution that were approved by a narrow majority of the electorate in a controversial referendum that he championed last year.

Under new presidential powers, Erdogan will have the authority to appoint top public officials as well as a vice president. The office of prime minister will be abolished and all executive power will be transferred to Erdogan alone.

The Venice Commission, which provides legal advice to the Council of Europe, warned about the changes in a report, saying they would "lead to an excessive concentration of executive power in the hands of the president and the weakening of parliamentary control of that power."

Omer, a 31-year-old taxi driver in Istanbul, told ABC News he was happy with the outcome.

"We always vote for our leader Recep Tayyip Erdogan," he said while navigating his cab through traffic. "Turkey is surrounded by enemies and countries in the west. The United States, France and Germany don't want us to be stable. In this election we have given them a strong message and a good old Ottoman slap."

Tapping in to nationalist fears of outside influences in Turkey after a failed coup in 2016, Erdogan painted his political opponents as traitors to democracy.

"There is no stopping for us until we bring Turkey, which we saved from plotters, coupists and political and economic hit men, street gangs and terrorist organizations, to among the top 10 economies in the world," he said.

Despite Erdogan's hopes for a strong economy, the value of Turkey's lire has lost nearly 20 percent of its value this year. That, coupled with high inflation rates and fears that the central bank's independence will be further reduced, has left international investors uneasy after Erdogan’s victory.