Around 61 million Iranians are eligible to vote in the polls where reformist Masoud Pezeshkian, 69, hopes for a breakthrough win against a divided conservative camp.
The Guardian Council, which vets candidates, allowed him to run against a field of conservatives now dominated by parliamentary speaker Mohammad Bagher Ghalibaf and former nuclear negotiator Saeed Jalili.
Also left in contention is cleric Mostafa Pourmohammadi after two ultraconservatives dropped out — Tehran major Alireza Zakani and Raisi's former vice president Amir-Hossein Ghazizadeh Hashemi.
«We start the elections» for the country's 14th presidential ballot, Interior Minister Ahmad Vahidi said in a televised address.
Iran's supreme leader Ayatollah Ali Khamenei cast his ballot shortly after the polls opened and urged Iranians to vote.
«Election day is a day of joy and happiness for us Iranians,» he said in a televised speech where he also called for a high turnout.
«We encourage our dear people to take the issue of voting seriously and participate,» he said.
The election in sanctions-hit Iran comes at a time of high regional tensions between the Islamic republic and its arch-foes Israel and the United States as the Gaza war rages on.
Polls opened at 8:00 am (0430 GMT) in 58,640 stations across the country, mostly in schools and mosques.
Polling stations will be open for 10 hours, though authorities could extend voting time as in previous elections.
Early projections of the