Of the eight candidates, the three frontrunners are former foreign ministers Abdullah Abdullah and Zalmay Rassoul and former finance minister Ashraf Ghani.
To win, a candidate must secure more than 50 percent of valid ballots, failing which the top two candidates go into a run-off. The three frontrunners all enjoy similar levels of support, so a second round of voting is likely.
Taliban insurgents launched a spate of attacks in the run-up to the vote, which they brand as a U.S.-backed sham, but there was no word of violence as voting got under way at 7 a.m. (0230 GMT) local time.
Here are some images from the election:
Afghan women stand in line while waiting for their turn to vote at a polling station in Mazar-i-sharif April 5, 2014. Voting was peaceful during the first few hours of Afghanistan's presidential election.
An Afghan woman casts her ballot while an electoral official reacts at a polling station.
An Afghan man tries to control his donkey loaded with ballot boxes and other election material to be transported to polling stations which are not accessible by road in Shutul, Panjshir province, a day before the election.
Fake election voter cards are photographed in Jalalabad April 3, 2014. The Taliban have launched a violent campaign to disrupt this weekend's presidential election in Afghanistan, but in a restive eastern corner of the country they are paying villagers to surrender their voting cards.
An election official uses an infrared light to check the thumb of a voter as the man dips his finger in ink before voting at a polling station in Kabul.
President Hamid Karzai casts his vote in Kabul.
Afghans wanting to vote queue in the rain outside a polling station before it opened in the capital city.
Afghan men search for their candidate on a ballot while voting during presidential and provincial elections at a polling station in Adraskan district of Herat province.
An Afghan policeman searches men before they enter a polling station.
An Afghan policewoman searches a woman before she enter a polling station in Mazar-i-sharif
An Afghan man searches for candidate on a ballot paper.