Turkish President Recep Tayyip Erdogan was on Sunday leading a tightly-contested presidential election in a partial count as he seeks a new mandate in the face of a revitalised opposition and weakening economy.

Turkish voters had for the first time cast ballots for both president and parliament in the snap polls, with Erdogan looking for a first round knockout and an overall majority for his ruling Justice and Development Party (AKP) to extend his 15-year grip on power.

In the presidential poll, Erdogan has just under 56 per cent against his nearest rival Muharrem Ince of the secular Republican People's Party (CHP) with almost 29 per cent, state-run Anadolu news agency said, based on a 60 per cent vote count.

Erdogan needs over 50 per cent to retain the presidency in the first round. But these are still partial results and the outcome could yet change drastically.

Trailing were Meral Aksener of the nationalist (Iyi) Good Party with over seven per cent and Selahattin Demirtas of the pro-Kurdish Peoples' Democratic Party (HDP) with under six per cent.

A count of almost 50 per cent for the parliamentary election also showed that Erdogan's ruling Justice and Development Party (AKP) - along with its Nationalist Movement Party (MHP) allies - were well ahead and set for an overall majority. But again this can change sharply.

The pro-Kurdish Peoples' Democratic Party (HDP) was hovering just under the 10 per cent minimum threshold needed to win seats, a factor likely to have a major impact on the composition of the new parliament.

'Protect your rights'

Erdogan had faced an energetic campaign by Ince, who has rivalled the incumbent's charisma and crowd-pulling on the campaign trail, as well as a strong opposition alliance in the legislative poll.

Ince vowed to spend the night at the headquarters of Turkey's election authority in Ankara to ensure a fair count and urged supporters to stay in polling stations until the final vote was counted.

The CHP said it had recorded violations in particular in the southeastern province of Sanliurfa, although Erdogan insisted, after voting himself, there was no major problem.

"I will protect your rights. All we want is a fair competition. Have no fear and don't believe in demoralising reports," Ince said after polls closed.

Erdogan has overseen historic change in Turkey since his Islamic-rooted ruling party first came to power in 2002 after years of secular domination. But critics accuse the Turkish strongman, 64, of trampling on civil liberties and autocratic behaviour.

Although Erdogan dominated airtime on a pliant mainstream media, Ince finished his campaign with eye-catching mass rallies, including a mega meeting in Istanbul on Saturday attended by hundreds of thousands of people.

The stakes are particularly high as the new president will be the first to enjoy enhanced powers under a new constitution agreed in an April 2017 referendum strongly backed by Erdogan.

As he cast his vote, Erdogan said the changes marked a "democratic revolution", although his opponents regard the most recent phase of his rule differently.

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.

'For the future'

Erdogan, whose mastery of political rhetoric is acknowledged even by critics, has won a dozen elections but is now fighting against the backdrop of increasing economic woes.

Inflation has zoomed well into double digits - with popular concern over sharp rises in staples like potatoes and onions - while the Turkish lira has lost some 25 per cent in value against the US dollar this year.

"At each election, I come with hope. But this year I have a lot more faith, but we'll see," said Hulya Ozdemiral as she cast her ballot in Istanbul.

But the opposition has lambasted the uneven nature of the poll, which saw state-controlled television ignore Ince's giant rally in Istanbul on the eve of the election.

And in a situation labelled as blatant unfairness by activists, the HDP's Demirtas has campaigned from a prison cell after his November 2016 arrest on charges of links to outlawed Kurdish militants.

After casting his ballot in his jail in the northwestern region of Edirne, Demirtas wrote on Twitter: "I wish that everyone uses their vote for the sake of the future and democracy of the country."

High security was in place across the country, with 38,480 police officers on duty in Istanbul alone. As is customary in Turkey on polling days, sales of alcohol were are also prohibited.