Turkey was at a "turning point" Monday, President Recep Tayyip Erdogan said after the opposition fighting his two-decade rule swept municipal elections in Istanbul, the country's emblematic megapolis, and other major cities.

Near-final results showed the main opposition Republican People's Party (CHP) wresting the main cities and Anatolian provinces that were strongholds for Erdogan's Islamic conservative AKP party.

Top urban centres Istanbul, capital Ankara, Adana, Bursa and Antalya were among municipalities to elect CHP mayors Sunday, less than a year after the knockback of a failed presidential challenge last May.

Observers called it Erdogan's worst election defeat since his party took power in 2002.

Many blamed inflation running at 67 percent and a crashing devaluation of the lira currency over the past year.

Pro-government dailies Hurriyet and Yeni Safah on Monday highlighted the voters' "message" to incumbents.

The result "can only be explained by the economy," wrote Abdulkadir Selvi, a commentator for pro-government daily Hurriyet seen as close to the Erdogan camp.

"A new wind has blown" through Turkey and the government now faces "a new political equation", he added.

Erdogan himself acknowledged a "turning point" and vowed to "respect the decision of the nation".

- 'Revolution at the ballot box' -

Secular nationalist daily Sozcu, which opposes Erdogan, splashed "revolution at the ballot box" across its front page, while major opposition paper Cumhuriyet hailed a "historic victory".

Victory for the CHP may have been expected in the economic and political capitals Istanbul and Ankara, which they claimed in 2019, but observers saw the broader anti-Erdogan surge as the strongest in almost 50 years, redrawing the electoral map.

Istanbul mayor Ekrem Imamoglu, the opposition's champion since taking the mayor's seat in Istanbul five years ago in a hard-fought battle, now looks set for a presidential run in 2028.

The vote "marks the end of democratic erosion in Turkey and the resurgence of democracy," Imamoglu told supporters overnight, saying his victory had "immense significance".

In Ankara, CHP mayor Mansur Yavas also bolstered his standing, topping his AKP opponent.

"We're going to see a race between Imamoglu and Yavas" for leadership, Hurriyet commentator Selvi wrote.

"Imamoglu is Erdogan's opponent in the country's next national elections," Soner Cagaptay of the Washington Institute posted on X.

The Istanbul mayor "has a chance to become Turkey's president... Turkey never fails to surprise - (the) game is on," he added.

Erdogan, who came to power as prime minister in 2003 before becoming president in 2014, said in early March that these municipal elections would be his last.

The 70-year-old leader told dismayed supporters overnight that they "must not waste" the four years remaining before the next presidential vote.