The election is taking place against the backdrop of raging inflation and massive devaluation, with the uncertainty weighing down on many voters, AFP correspondents reported.

"Everyone is worried about the day to day," said Guler Kaya at an Istanbul polling station.

"The crisis is swallowing up the middle class, we have had to change all our habits," said the 43-year-old. "If Erdogan wins, it will get even worse," she added.

In the capital Ankara, Meliha Sonmez sounded a warning as she prepared to vote: "This election is not just municipal."

"If Erdogan loses the ballot, he will be weakened," said the retired woman in her 60s who lost 32 relatives in the devastating February 2023 earthquake in Hatay.

Erdogan may not be a candidate in the municipal vote, but he has dominated the campaign.

His road to power in Turkey began in Istanbul when he was elected mayor of the mythic city straddling Europe and Asia in 1994.

His allies held the city until five years ago, when Ekrem Imamoglu of the secular Republican People's Party (CHP) wrested control.

As soon as Erdogan clinched re-election as president last May -- he has held the position since 2014 -- he launched the battle to reclaim the city of 16 million people.

"Istanbul is the jewel, the treasure and the apple of our country's eye," the 70-year-old leader said at a recent rally in the city.

"Whoever wins Istanbul, wins Turkey," Erman Bakirci, a pollster from Konda Research and Consultancy, recalled Erdogan once saying.

- 'Emotional day' -

After casting his vote with his wife and two sons in Istanbul around midday Sunday, Imamoglu emerged to applauding chanting "Everything will be fine", his 2019 election slogan.

"I hope that... the will of the ballot box will be expressed without harm to anyone, whatever the result is, whoever our citizens voted for," Imamoglu said in the garden of a school polling station.

"Today is an emotional day for me", he said, adding that he was trying to ensure "equality without prioritising partisanship".

"We are doing our best to ensure that young people, women and mothers have the best possible life," he said.

Armed clashes were reported from a village in Turkey's Kurdish-majority southeast, leaving one dead and 12 wounded, a local official told AFP.

- More than a mayor's race -

The Turkish president has named former environment minister Murat Kurum as his candidate for Istanbul mayor.

The 2019 vote was controversially annulled, but Imamoglu won the re-run vote by an even greater margin, which turned him into an instant hero for Turkey's notoriously fractured opposition and a formidable foe for Erdogan.

If Imamoglu manages to retain the Istanbul mayor's seat, he'll likely be the main challenger to the ruling party in the next presidential elections, set for 2028.

The election is being held with inflation at a whopping 67 percent and with a massive devaluation of the lira, which slid from 19 to a dollar to 31 to a dollar in one year. Analysts say this could work in favour of the opposition.

Erdogan threw all his energy into campaigning for his candidate, repeatedly telling rallies that Imamoglu, whose name he never mentions, is a "part-time mayor" consumed by presidential ambitions.

Imamoglu focused his campaign on local issues and defended his achievements in office.

"Every vote you give to the CHP will mean more metros, creches, green spaces, social benefits and investment," he promised ahead of the vote.

- Fractured opposition -

Some 61 million voters are picking mayors across Turkey's 81 provinces, as well as provincial council members and other local officials.

The opposition has been fractured ahead of the polls, in contrast with the local elections five years ago.

This time around the main opposition party, the social democrat CHP, has failed to rally support behind a single candidate.

Polls opened at 0400 GMT in the east of the country and were due to close at 1400 GMT in the west, including Istanbul.

The first estimates are expected to be released late on Sunday.