Afghans voted in presidential elections amid tight security on Saturday, even as insurgents attacked polling centres in a series of blasts and clashes across the country that left at least two people dead.

The first-round vote marks the culmination of a bloody election campaign that despite a large field of candidates is seen as a close race between President Ashraf Ghani and his bitter rival Abdullah Abdullah, the country's chief executive.

Wary authorities placed an uneasy Kabul under partial lockdown, flooding streets with troops and banning trucks from entering the city in an effort to stop would-be suicide bombers targeting residents as they cast their votes.

Polls closed at 5:00pm (1230 GMT) after a two-hour extension due to long queues of people still waiting to vote, the Independent Election Commission said.

Compared to previous elections, the initial toll appeared relatively light, though authorities provided little information about reported blasts and ongoing armed clashes with the Taliban in various provinces.

A security official who requested anonymity told AFP that two civilians had been killed and 27 wounded in Taliban bombings and mortar attacks at polling centres across the country.

Serious security incidents were reported in several provinces including Kunduz, Nangarhar, Kabul, Bamiyan and Kandahar.

The Taliban, who unleashed a string of bombings during the two-month election campaign, claimed to have conducted hundreds of attacks against Afghanistan's “fake elections”.

Ghani, having voted at a Kabul high school, said the most important issue was finding a leader with a mandate to bring peace to the war-torn nation.

“Our roadmap (for peace) is ready, I want the people to give us permission and legitimacy so that we pursue peace,” said Ghani, who is seeking a second term.

Some 9.6 million Afghans are registered to vote, but many lack faith that after 18 years of war any leader can unify the fractious country and improve basic living conditions, boost the stagnating economy or bolster security.

Observers from the Afghanistan Independent Human Rights Commission said turnout appeared to be low, especially among women.

Still, many voters braved insurgent attacks and long queues to cast a ballot.

“I know there are security threats but bombs and attacks have become part of our everyday lives,” 55-year-old Mohiuddin, who only gave one name, told AFP.

“I am not afraid, we have to vote if we want to bring changes.”

Abdullah and Ghani both claimed victory in the 2014 election — a vote so tainted by fraud and violence that it led to a constitutional crisis and forced then-US president Barack Obama to push for a compromise that saw Abdullah awarded the subordinate role.

“The only request I have from the election commission is that they ensure the transparency of the election because lots of people have lost their trust,” said Afghan voter Sunawbar Mirzae, 23.

Problems voting

Voting in Afghanistan's fourth presidential election was supposed to take place at some 5,000 polling centres across the country but hundreds were closed due to the security situation.

Many Afghans said voting went smoothly, triumphantly holding up fingers stained in indelible ink to show they had cast a ballot, but several said they had experienced problems.

“I came this early morning to cast my ballot. Unfortunately my name was not on the list,” said Ziyarat Khan, a farmer in Nangarhar. “The whole process is messy like the last time.”

Campaigning was hampered by violence from the first day, when Ghani's running mate was targeted in a bomb-and-gun attack that left at least 20 dead.

Bloody attacks have continued to rock Afghanistan, including a Taliban bombing at a Ghani rally last week that killed at least 26 people in the central province of Parwan near Kabul.

The interior ministry said it had deployed 72,000 forces to help secure polling stations.

Election officials say this will be the cleanest election yet, with equipment such as biometric fingerprint readers and better training for poll workers to ensure the vote is fair.

Still, the US embassy in Kabul has said it is “disturbed by so many complaints about security, lack of an equal playing field and fraud”.

Saturday's poll was initially slated to take place in April, but was twice delayed because election workers were ill-prepared, and the US was leading a push to forge a withdrawal agreement with the Taliban.

That deal has been scuppered for now after US President Donald Trump pulled out, and Afghanistan's next president will likely face the daunting task of trying to strike a bargain with the Taliban.

Results are not expected until October 19. Candidates need more than 50 per cent of the vote to be declared the outright winner, or else the top two will head for a second round in November.

Pakistan extends congratulations

Pakistan congratulated the Afghanistan government and the people for successfully holding the 4th presidential elections "despite serious hurdles and challenges", a statement by the Foreign Office said.

"The people of Afghanistan particularly deserve appreciation for their clear decision to continue with the democratic course," said the statement.

Pakistan expressed hope that with the new government, the stalled peace process can be moved forward to bring an "Afghan-led and Afghan-owned negotiated political settlement" to the 18-year-old conflict in Afghanistan.

"Pakistan will continue to facilitate the new Afghan government towards this end," the Foreign Office said in its statement.

The statement also stressed that a "strong, independent, peaceful and prosperous Afghanistan" is key to regional peace and stability.