Afghan presidential election: Heavy security as polls open
More than 70,000 security forces have been deployed across the country to counter Taliban militants who have vowed to target polling stations.
The twice-delayed vote is taking place after Taliban-US peace talks collapsed earlier this month.
The two main candidates are the incumbent, Ashraf Ghani, and chief executive, Abdullah Abdullah.
They have shared power since 2014 in a unity government.
At least one person has been killed and 27 others wounded in bomb and mortar attacks on voting centres.
But in the southern city of Kandahar, women were seen standing in queues to vote, despite a bomb attack on a polling station.
Women voters make up 35% of the more than nine million Afghans registered to vote.
Turnout is expected to be low, but one voter said she would cast her vote even if it meant standing in long queues for hours.
"Bravery is defined when one musters the courage to cast their vote in Afghanistan," said Roya Jahangir, a doctor based in the capital, Kabul.
"We hope this time there is no fraud - otherwise voters will feel cheated once again," she told Reuters news agency.
Afghanistan's next president will lead a country devastated by four decades of war. The conflict continues to kill thousands of people every year, drawing in forces from around the world.
Who are the contenders?
Eighteen men - including former warlords, ex-spies and members of the country's former communist government - initially put themselves forward to fight the election, but five have dropped out.
Not one woman is running for president, and only three women appear on the tickets of others.
Almost 5,000 polling stations will be open on Saturday for people to cast their votes.
A biometric voting system - based on fingerprints - will be used across the country to try to avoid fraud as people cast their ballots.