Iranian supreme leader Ayatollah Ali Khamenei cast the first vote indicating the opening of country's presidential election, according to a CNN report.

"Each vote counts ... come and vote and choose your president ... this is important for the future of your country," Khamenei said after casting his vote, according to the report. "Low turnout will increase the pressure of the enemies."

The election is likely to deliver a hardline president who lost the 2017 election and has headed the country's judiciary for the last two years, said the report.

Judicial Chief Ebraham Raisi, a close associate of Khamenei, is the uncontested frontrunner, who emerged after the country's election supervisory body known as the Guardian Council stopped almost all the serious candidates from the race, the CNN report said.

The disqualifications have been condemned countrywide and even Khamenei criticized some of them and called the rejections "unjust".

The new government will be faced with a number of challenges, including overcoming an economic crisis fuelled by Covid-19, calls for constitutional reforms and coming up with a solution to deal with growing questions  surrounding the succession plans for Khamenei, 81, who has the final say in all Iranian affairs.

Iran is also in the midst of negotiations with the United States about ways to revive the 2015 nuclear deal.

The CNN report said that the spiralling queues stretching outside the polling stations mostly had conservative voters.

Many were seen carrying posters of Iran's slain top general Qasem Soleimani, killed in Baghdad following former US President Donald Trump's orders.

There have been calls for reforms to allow change in leadership and the heavily engineered election has left many in dismay.

Some quarters have opposed the elections which they perceive as a fresh attempt by Iran clerical rulers to maintain their control.

Many people, including young voters have said they are not going to vote despite the authorities trying to convince them that they should vote for the sake of the welfare of the country.

Most national polls, too, have predicted less than 50 per cent voter turnout in the presidential election since the establishment of the Islamic Republic in 1979.

Fearing increasing voter apathy, Khamenei made a last minute appeal to the electorate on Thursday, asking them to come out and vote. He warned the voters that refusal to vote would play into the hands of the enemies of Iran and destabilize the country. 

"Enemies seek to undermine participation of people in elections to weaken Iran," Khamenei said in a televised speech, according to the CNN report.

"If there is less participation and if the country is weakened then they can cause insecurity in the country...if we have less participation by the people we will have more pressures exerted by our foes...economic pressures," the leader added, it said.

"The solution is to increase people's participation and show the enemy that people are participating," he emphasised.

Earlier, Khamenei had also warned that blank votes would be considered a "sin", the CNN report stated.

Raisi also urged people to cast their vote. He wrote in a tweet : "It's the right of the people to be upset and perhaps some have been upset by the current situation, but I'm asking all of the Iranian people to come to the polls to solve the problems."

"I hope that people will feel the change soon ... I consider myself a servant for all of the people of Iran," Raisi also said according to Iran's semi-official Tasnim news agency, CNN reported.