Iran closed the polling stations but voters already queuing up were allowed to cast their ballots. Polls were originally due to close at 6 p.m. local time (1330 GMT) but polling stations were ordered by the Interior Ministry to remain open until 10 p.m. as voters continued to stream to polling stations.
Initial results are not expected for at least 12 hours.
Iran's Interior Minister Sadeq Mahsouli estimated the turnout is expected to be above 70 percent.
In Washington, US President Barack Obama has welcomed the enthusiasm shard among the Iranians as they go to polls. "We are excited to see what appears to be a robust debate taking place in Iran," Obama stated, according to AFP.
"Obviously after the speech that I made in Cairo, we tried to send a clear message that we think there's the possibility of change, and, you know, ultimately the election is for the Iranians to decide," Obama went on to say. "Whoever ends up winning the election in Iran, the fact that there's been a robust debate hopefully will help advance our ability to engage them in new ways," Obama said.
