Long queues as Iranians start voting in presidential election following divisive campaign

Iranians began voting on Friday in a closely-fought presidential contest between pragmatist President Hassan Rouhani and hardline challenger Ebrahim Raisi that could determine the pace of social and economic reform and Iran's re-engagement with the world.

State television showed long queues outside polling stations in several cities and said 56 million Iranians out of the more than 80 million population were eligible to vote

Polling for 55 million voters started at 8:00am after a campaign that became increasingly bitter the longer it went on. Echoing recent elections around the world, it centered on populist claims that ordinary people were being left behind.

President Hassan Rouhani's policy of opening up to the world and efforts to rebuild the stagnant economy faced stiff competition from hardline cleric Ebrahim Raisi, 56, who has positioned himself as a defender of the poor and called for a much tougher line with the West.

Rouhani, a 68-year-old moderate cleric, has sought to frame the election as a choice between greater civil liberties and "extremism".

He has pushed the boundaries over the past fortnight, criticising the continued arrest of reformist leaders and activists, and calling on security agencies not to interfere in the vote.

Raisi says he will stick by the 2015 nuclear deal with world powers, that saw curbs to Iran's atomic programme in exchange for sanctions relief, but he points to the continued economic slump as proof that Rouhani's diplomatic efforts have failed.

"Instead of using the capable hands of our youths to resolve problems, they are putting our economy in the hands of foreigners," Raisi said at a final rally in the holy city of Mashhad on Wednesday.

Rouhani responded by calling on voters to keep hardliners away from Iran's delicate diplomatic levers.

"One wrong decision by the president can mean war and a correct decision can mean peace," he said at his own Mashhad rally.

"Everyone should vote in this important election ... vote at early hours," supreme leader Ayatollah Ali Khamenei said after casting his vote in the capital Tehran.

"The country's fate is determined by the people."

Polls close at 6:00pm, although authorities often extend voting into the evening. Ballot counting will start at midnight and final results are expected within 24 hours of polls closing, the semi-official Fars news agency said. The elections are also for city and village councils.

The election comes at a tense moment in US-Iran relations.

Rouhani gained a reprieve on Wednesday when the administration of US President Donald Trump agreed to continue waiving nuclear-related sanctions, keeping the deal on track for now. But Trump has launched a 90-day review of the accord that could see it abandoned, and is visiting Iran's bitter regional rival Saudi Arabia this weekend.