Voting in Iran's parliamentary election has been extended by two hours because of a high turnout, state media report.
It is the first poll since mass opposition protests were sparked by Mahmoud Ahmadinejad's disputed presidential election victory in 2009.
The vote is widely viewed as a contest between his supporters and those of Supreme Leader Ayatollah Ali Khamenei.
The opposition Green Movement is not taking part. Its leaders have been under house arrest since February 2011.
Early on Friday, Iranian TV broadcast images of Ayatollah Khamenei casting his vote in the capital, Tehran. He said it was a "duty and a right'' for Iranians to elect members of the 290-seat parliament, the Majlis.
"Because of the controversies over Iran and increased verbal threats the more people come to the polling stations the better for the country."
"The vote always carries a message for our friends and our enemies.''
A spokesperson for the Guardian Council, which vets and approves parliamentary candidates, told Iran's state-run Arabic-language TV channel, al-Alam, that turnout in the first three hours had exceeded that achieved in previous elections.
State TV broadcast pictures from several polling stations in Tehran and the provinces, showing long queues. A commentary said they were a "disappointment to the bad-wishers".
Later, al-Alam reported that voting had been extended for two hours because of "high turnout", and that polling stations would close at 20:00 local time (16:30 GMT). Official results are expected on Sunday or Monday.
More than 48 million people are eligible to take part in the election, which is taking place at about 47,000 polling stations.
But correspondents say even some of Mr Ahmadinejad's supporters are quietly calling for voters to stay away.
He has fallen out with Ayatollah Khamenei in recent months, and some of his supporters complain that their candidates have been barred from standing by the Guardian Council, which is controlled by the supreme leader.
Last April, Mr Ahmadinejad decided to sack his intelligence minister, reportedly after he had dismissed an official with close ties to the president's chief of staff and close confidante, Esfandiar Rahim-Mashaei.
But Ayatollah Khamenei decided to overrule him and ordered the minister's reinstatement. The decision is said to have so enraged Mr Ahmadinejad that he stayed away from government meetings for 11 days
The respective strength of the different conservative camps after this poll will define the balance of power for what may be a much more important vote - the 2013 presidential election, says BBC Iran correspondent James Reynolds.
However, the results of the elections are unlikely to change Iran's stance on its controversial nuclear programme, he adds.
Voters in Tehran who spoke to the BBC said they are angered both by the new sanctions imposed by the US and EU on Iran's oil and banking industries over its continued refusal to halt its uranium enrichment programme, and also by what they see as their government's mismanagement of the economy.
Former President Akbar Hashemi-Rafsanjani, a rival of Mr Ahmadinejad, said that a "good parliament" would emerge if the ballots were properly counted.
"God willing, the outcome of the elections will be what the people want,'' he told reporters when casting his vote in Tehran.
No independent observers are monitoring the voting or checking the turnout figures or results.