CNN's Erin Burnett reports from inside Iran. Watch live from Tehran on CNN at 7 p.m. ET.  (CNN) -- Television cameras zoomed in on his hand Friday as Iran's supreme leader filled out the first ballot in the national election to replace outgoing President Mahmoud Ahmadinejad.  Ayatollah Ali Khamenei slipped the folded paper into the ballot box and turned to the cameras. His vote officially opened the ballots as he called on the 50 million Iranians eligible to vote to pick one of six candidates in the "epic" election.  "My expectation of our endeared people is for everyone to take part, and I would recommend that they go to ballot boxes as soon as possible and not to delay," he said.  Iranians appeared to heed their leader's call, with voters flocking to the country's 60,000 voting stations.  Who's running for Iran's presidency?  Who's running for Iran's presidency?  Who's running for Iran's presidency?  Who's running for Iran's presidency?  Who's running for Iran's presidency?  Who's running for Iran's presidency?  The six candidates also have cast their votes, according to Iran's state-run IRNA news agency.  They are: Mohammad Bagher Ghalibaf, Ali-Akbar Velayati, Saeed Jalili, Mohsen Rezaei, Hassan Rouhani, and Mohammad Gharazi.  Velayati, Ghalibaf and Jalili, who is Iran's chief nuclear negotiator, are considered close to Khamenei and would be unlikely to challenge his authority. Of the three, Jalili has seen the most popular support going into the vote.  Rouhani is considered a centrist and has the backing of the highly influential former President Akbar Hashemi Rafsanjani.  CNN's view on the streets of Tehran  The Interior Ministry voting hours extended to accommodate a high turnout, state-run Press TV said. The polls closed at 11 p.m. (2:30 p.m. ET). Voter turnout is expected to hit 70 percent, the ministry said, and votes are already being counted, Press TV said.  The head of the Election Committee of Tehran Province said the voter turnout was predicted to hit 70% in the province, the channel reported.  After the Green Movement uprising that flooded Tehran's streets following Ahmadinejad's re-election in 2009, the government has accused the West of urging some voters to boycott the polls.  Hours into the voting, Rouhani complained of a voting irregularity. A reform candidate, Mohammed Aref, who dropped out of the race earlier in the week, is still on some ballots.  Rouhani is worried that voters may mistakenly select Aref, which would amount to a vote thrown away. It was not clear how many ballot papers were concerned.  Iran's semi-official Mehr News reported via Twitter that voting lines got longer in the afternoon, and that there were insufficient voting slips in some polling stations.  CNN's Erin Burnett on 2013 vs. 2009 elections  Images of bleeding and dying Iranians flickered across social media four years ago after allegations of election fraud sparked protests and clashes. Police and the Basij, a feared paramilitary group, cracked down on the protests.  Protesters were jailed, and human rights groups alleged many were tortured and killed behind bars while the government quashed the uprising.  Reform politicians representing the movement, including Ahmadinejad's election rival, former Prime Minister Mir Hossein Moussavi, have remained under house arrest.  Despite the unrest, Ahmadinejad's re-election was formally certified by the clerical establishment.  Ahead of the vote this time round, campaigning was more muted although  Khamenei's office repeated his call to the ballot boxes Friday with posts on social networking site Twitter.  "I humbly expect from our nation to participate all in #IranElection & do this as soon as possible," the supreme leader's post said.  Voting is not mandatory in Iran, but there are major incentives to push people to the polls. An active voter has a better shot at promotions in the workplace and preference when it comes to collecting social welfare benefits.  This can be vital in an economy that is chronically weighed down by international sanctions over nuclear concerns.  Khamenei also tweeted a jab at the United States, which has often led the charge to tighten those sanctions.  "I have heard that #USpoliticians said they don't recognize #IranianElection. Hell with their recognition!" he said.  Rights group Amnesty International said this week that it was "concerned by evidence that the Iranian authorities are intensifying their clampdown on dissent" in the run-up to the vote.  "Those targeted include political activists, journalists and other media workers, trade unionists, advocates of greater rights for Iran's religious and ethnic minorities, students and others. In many cases, the full reasons for arrest and detention are not known; in others, those arrested have been brought before the courts on sweeping but vaguely worded charges, convicted and sentenced to prison terms," it said.  The head of language services for BBC World Service, Liliane Landor, also complained Thursday of "unacceptable harassment" of its staff and other independent journalists in Iran.  "The BBC is very concerned by the unprecedented levels of intimidation being suffered by families of BBC Persian Service staff living in Iran in the final days of the presidential election campaign," she said.  "The harassment has included threats that relatives will lose jobs and pensions and be prevented from traveling abroad. For the first time the lives of BBC Persian TV staff living in the UK have also been threatened."  Iran's Minister of Culture and Islamic Guidance, Mohammad Hosseini, said more than 2,000 local reporters and 450 foreign journalists were covering the election in Iran.  The head of the Foreign Reporters Bureau within the ministry, Alireza Shirvani, said the number of foreign reporters covering the presidential election had increased by about 15% compared with four years ago.  All candidates are preapproved to run for the nation's highest elected office by Iran's Guardian Council, a nonelected body made up of six clerics and six lawyers operating under the oversight of the supreme leader.  It allows Khamenei to limit the election process. Out of 680 candidates, eight were approved. Two subsequently dropped out of the race.  In a blow to Ahmadinejad, his aide and protege Esfandiar Rahim Mashaei was among those excluded by the Guardian Council.  Since his reelection, conservative politicians close to the supreme leader have assailed Ahmadinejad for being too liberal, and he has often been at odds with Khamenei.  Some of Ahmadinejad's associates have faced heavy repression, and hardliners attempted to link the president to the largest embezzlement case in the country's history.  CNN's Azadeh Ansari contributed to this report.
Ayatollah Khamenei casts his ballot and urges 50 million Iranians to vote for one of six pre-approved candidates.