Tight security ensured Afghanistan's presidential election was held on Saturday in relative calm, though several small attacks, low turnout and complaints about the voting system heightened fears an unclear result could drive the country into further chaos.

Preliminary results are not expected before October 17 and final results not until November 7. If no candidate gets 51 per cent of the vote, a second round will be held between the two leading candidates.

Taliban fighters attacked several polling stations across the country to try to derail the process, but intense security prevented the large-scale violence of previous polls.

“This election was the healthiest and fairest election in comparison to the previous elections,” said Hawa Alam Nuristani, head of country's Independent Election Commission (IEC), after the voting concluded.

Ten of thousands of Afghans braved the threat of militant attacks and delays at polling booths to vote in the election, a major test of the Western-backed government's ability to protect democracy against Taliban attempts to derail it.

Two policeman and one civilian were killed in mostly small-scale Taliban attacks, the defence ministry said, adding 37 people were injured.

Tens of thousands of troops were deployed to try to protect voters and polling stations.

IEC officials did not immediately share the details on turnout, but Western diplomats in Kabul estimated it was low due to fears of violence and delays caused by polling officials.

Voting was extended by two hours, after technical problems delayed the opening of some polling stations around the country.

Independent election observers and activists said a slow pace to voting triggered confusion at some polling stations, with long queues forming outside.

“It took the first voter 31 minutes to vote. For subsequent voters it was taking around five minutes and then it started to streamline to 3 minutes and 30 seconds,” said Nishank Motwani, an observer stationed in Kabul.

“Election commission staff looked panicked and voters were getting angry that the queue was not moving.”