Opposition supporters on Sunday filled an Istanbul square to celebrate the re-election of Ekrem Imamoglu as mayor, who dealt a second blow to President Recep Tayyip Erdogan's ruling party by repeating his landmark 2019 win.
Partial results from across the nation of 85 million people showed major advances for the Republican People's Party (CHP) at the expense of Erdogan's Justice and Development Party (AKP).
Istanbul's mayor, the opposition's Ekrem Imamoglu, claimed re-election with nearly all ballot boxes opened, telling a euphoric crowd of supporters: "Tomorrow is a new spring day for our country."
Final results are expected to be released on Monday by the country's electoral commission.
Erdogan, 70, had launched an all-out personal campaign to win back Istanbul, the economic powerhouse where he was once mayor. Rampant inflation and an economic crisis have, however, hit confidence in the ruling party.
Large crowds filled the square outside the opposition party's Istanbul city headquarters waving Turkish flags and lighting torches to celebrate the result.
After casting his vote, Imamoglu emerged to applause and chants of "Everything will be fine", the slogan he used when he first took the city hall from the AKP in 2019.
The 52-year-old is increasingly seen as the biggest rival to Erdogan's AKP ahead of the next presidential election in 2028.
In Ankara, mayor Mansur Yavas -- also of the CHP -- claimed victory in front of large crowds of supporters, declaring "the elections are over, we will continue to serve Ankara".
"Those who have been ignored have sent a clear message to those who rule this country," he added.
Yavas led with 58.6 percent of the vote to 33.5 percent for his AKP opponent, with 46.4 percent of ballot boxes opened.
Opposition supporters celebrated victory in Izmir, Turkey's third-largest city, as well as in the southern city of Antalya.
Some AKP stronghold towns were at risk of being lost, results indicated.
"Voters have chosen to change the face of Turkey," said CHP chairman Ozgur Ozel as the results emerged.
"They want to open the door to a new political climate in our country."
Erdogan acknowledged the electoral setback in a speech to supporters at the headquarters of his party.
"Unfortunately, we have not obtained the results that we wanted," he told a subdued crowd.
"We will of course respect the decision of the nation. We will avoid being stubborn, acting against the national will and questioning the power of the nation," he added.
Erdogan has been president since 2014 and won a new term in May last year. He had called Istanbul the national "treasure" when launching his campaign to retake the city.
But while he dominated the campaign, his personal role did not help overcome the widespread concerns over the country's economy.