President Hamid Karzai, the frontrunner, is vying for re-election against about 30 candidates, including two women.

Former foreign minister Abdullah Abdullah, former finance minister Ashraf Ghani and former planning minister Ramazan Bashardost are the main challengers to Karzai. In the past, all three have served in his government.

Voters are also electing 420 provincial council members spread out over the country's 34 provinces.

Death threats

Taliban militants vowed to disrupt the vote and have threatened to slit the throats and chop off fingers of anyone who votes on Thursday.

Afghan and NATO military officials offered assurances that more than 100,000 international troops and around 200,000 Afghan forces were on high alert and were prepared to neutralize any attack that might be mounted by the Taliban.

In Kabul, shops and business were closed and round-the-clock squads of extra police checked the few cars on the roads.

President Hamid Karzai called on Afghans to defy Taliban threats and vote in the election, which could prove the toughest test yet of his own mandate and his nation's fragile democracy.

"Enemies will do their best, but it won't help," he told reporters late on Wednesday.

Global support

More than 270,000 election observers, including 2,000 from abroad, are overseeing the balloting at more than 6,500 polling centres, while the commission said it was unable to open voting stations in nine districts that remain outside government control.

Polling stations opened at 9:30 am local time (0500 UTC) and voting is to continue until 4 pm (1130 GMT). Results are not expected until about 48 hours after the polls are closed, according to the Independent Election Commission.

While Karzai leads in recent opinion polls, he is not expected to receive more than 50 percent to win the elections outright. If no candidate posts a first-round majority, a run-off would be held around first week of October.

mrh/dpa/AFP

Editor: Nigel Tandy