An explosion has occurred near a polling station in the Afghan city of Kandahar, just an hour after voters began queuing to cast their vote to elect a new president.

A senior provincial government official said three people were injured by the blast.

No militant group has claimed responsibility.

The Taliban, which controls more of the country than at anytime since its regime was toppled in 2001, has threatened voters to stay away from the election or risk being hurt.

There are 14 candidates registered in the election race - but the leading contenders are incumbent President Ashraf Ghani and his former deputy Abdullah Abdullah.

Wounded Afghans lie on a bed at a hospital after a bomb attack on a local mosque in Kandahar province, south of Kabul, Afghanistan | Image: STR/AP/Press Association Images

The winner will play a crucial role in the country's quest to end the war with the Taliban and the resumption of talks between the hardline insurgents and the United States that were called off earlier this month.

Fear and frustration at the relentless corruption that has characterised successive governments ranks high among the concerns of Afghanistan's 9.6 million eligible voters.

Tens of thousands of police, intelligence officials and Afghan National Army personnel have been deployed throughout the country to protect the 4,942 election centres.

Authorities said 431 polling centres will stay closed because it was impossible to guarantee their security since they were either in areas under Taliban control or where insurgents could threaten nearby villages.