The candidates differ on some issues such as the country's border dispute with Pakistan. But all preach against fraud and corruption and vow to improve security.
Polls were due to close at 4 p.m. local time (1130 GMT), but a spokesman for the Independent Election Commission, Noor Mohammad Noor, said polling stations could be kept open on a case-by-case basis to allow everybody in line to vote.
Mohammad Daoud Sultanzai, another presidential candidate, said election day was a time for the Afghan people to raise their voice and play a role in making decisions about their country.
Sultanzai appeared on television with his wife at his side, a rare occurrence in a country where male and female voters are segregated.
“Today is a historical day for Afghanistan,” his wife, Zohra, said. “It is a big honor that I have participated in this process and I ask all Afghan mothers, sisters and daughters to participate in this political process and have an active role in the election.”
Women have played a more visible role in this election than in the past as concern is rising that women will lose much of the gains they have made after international forces withdraw, reducing the ability of the U.S. and other Western countries to pressure the government to work for equality.
Electoral officials have taken extra measures to prevent fraud after widespread vote-rigging in 2009 marred Karzai's re-election.
Strict protocols include bar codes on the ballot boxes being delivered to nearly 6,500 polling centers in all 34 provinces and plans to tally the results immediately after the vote closes and post a copy of the results at each center.
