There have been at least five explosions in Afghanistan's capital as Afghans head to the polls to elect their new president.

The Taliban's threat to scupper the country's second presidential and provincial elections seems to be paying off, with voter turnout apparently running low due to fears of violence and reprisals.

Incidents in Kabul include a rocket landing close to voters, a suicide attack, and a stand-off between Afghan police and five suspected Taliban suicide bombers.

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Afghan women stand in line as they wait for the opening of a polling centre in Kabul this morning, defying the Taliban's orders not to vote

Some polling stations have been closed due to scattered rocket and bomb attacks, affecting the vote for Afghanistan's new President.

Low turnout in the south would harm President Hamid Karzai's re-election chances and boost the standing of his top challenger, former Foreign Minister Abdullah Abdullah.

Turnout in the north appeared to be high, a good sign for Abdullah.

International officials have predicted an imperfect election - Afghanistan's second-ever direct presidential vote - but expressed hope that Afghans would accept it as legitimate, a key component of President Barack Obama's war strategy.

A U.N. spokesman said there were no early reports of widespread irregularities, though ahead of the vote, the country had been buzzing with rumors of ballot-stuffing, bogus registrations and trafficking in registration cards on behalf of Karzai - allegations his campaign has denied.

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Women are searched with a metal detector as they queue to enter a polling station in Kabul today

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An Afghan woman holds up her ink-stained finger and her ID card after voting, left, while right, another woman's burka billows out as she strides away from the polling booth after voting

Taliban militants, though, pledged to disrupt the vote and circulated threats that those who cast ballots will be punished, which appeared to dampen turnout.

An Associated Press reporter who visited six polling centres in Kabul said he saw no lines at any of them, and a voting official in Kandahar, the south's largest city and the Taliban's spiritual birthplace, said voting appeared to be 40 percent lower than during the country's 2004 presidential election.

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An election worker holds up a ballot paper. With many illiterate voters, the candidates are also also denoted by their own personal symbol - including an axe, an apple, and an alarm clock

The official asked not to be identified because he wasn't authorised to release turnout figures.

Scattered reports of violence trickled in from around the country, including a rocket that landed near voters in Helmand and an explosion at a voting site in Kabul.

Security companies in the capital reported at least five blasts, and Kabul police exchanged fire for more than an hour with a group of armed men, including a suicide bomber who blew himself up.

Karzai, dressed in his traditional purple and green striped robe, voted at 7 a.m. at a Kabul high school. He dipped his index finger in indelible ink - a fraud prevention measure - and held it up for the cameras. Presidential palace officials released a rare photo of Karzai's wife casting her vote.

'I request that the Afghan people come out and vote, so through their ballot Afghanistan will be more secure, more peaceful,' Karzai said. 'Vote. No violence.'

Karzai, who has held power since the Taliban was ousted in late 2001 by a U.S.-led invasion, is favored to finish first among 36 official candidates, although a late surge by Abdullah could force a run-off if no one wins more than 50 percent.

Preliminary results were expected to be announced in Kabul on Saturday.

The top U.N. official in the country, Kai Eide, acknowledged scattered attacks but said the election 'seems to be working well.'

A U.N. spokesman said there were no early reports of widespread irregularities.

However, presidential candidate Ramazan Bashardost, who had 10 percent support in pre-election polls, said he washed off the supposedly indelible ink and called on authorities to 'immediately stop this election.'

'This is not an election, this is a comedy,' Bashardost said.

Militants carried out a string of assaults around the country.

In northern Baghlan province, insurgent attacks closed 14 polling sites, and the police chief of Old Baghlan city and several police were killed, said Abdul Malik, the provincial election director.

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Afghan police drag the bodies of two gunmen killed in a gunfight in Kabul today as security forces struggled to protect civilians going to the polls

'Some of the stations are open, with the presence of our personnel, but there is no one coming to vote. I told them to wait until the end of the day before coming back,' Malik said.

An AP reporter in southern Helmand province said more than 20 rockets had landed in the capital of Lashkar Gah, including one near a line of voters that killed a child.