"The blast took place close to a polling station which is a school building and wounded four voters, one critically," Abdul Hameed, governor of the province's Mohammad Agha district, told Reuters on Saturday.

Afghans braved the threat of Taliban violence to vote for a successor to President Hamid Karzai in a landmark election held as US-led forces wind down their lengthy military invasion of the war-ravaged nation.

The country's third presidential election brings an end to over 12 years in office by President Karzai, who has held power since the Taliban were ousted by invading US-led forces in December 2001, first as an interim president and then nationally elected into office in 2004. He won a second presidential term in 2009.  

Long queues formed outside polling stations in cities across the country, despite cold and wet weather, as voters cast their ballots at around 6,000 centers under tight security.

The Taliban have rejected the election as a foreign plot and urged their militants to attack polling staff, voters and security forces, but only one incident was reported in the first few hours of voting.

In Kabul, hit by a series of deadly attacks during the election campaign, hundreds of people lined up in the open air to vote despite the insurgents' promise of violence.

"I'm not afraid of Taliban threats, we will die one day anyway. I want my vote to be a slap in the face of the Taliban," housewife Laila Neyazi, 48, told AFP.

Poll security was a major concern following the attacks in Kabul, most recently a suicide bombing on Wednesday that killed six police officers.

Interior Minister Omar Daudzai said all 400,000 of Afghanistan's police, army and intelligence services were being deployed to ensure security around the country.

NTJ/MB