Afghan President Ashraf Ghani speaks after casting his vote in the presidential election in Kabul, Afghanistan on Saturday. Photo: VCG

Afghanistan's President Ashraf Ghani appeared to have won a second term on Sunday, ­narrowly scoring an outright win in preliminary polling results, but his main rival immediately vowed to challenge the tally.

After months of political limbo and bitter allegations of fraud and corruption in the September 28 poll, Afghanistan's Independent Election Commission said Ghani had won 50.64 percent of the vote.

If it holds, the result is enough for Ghani to avoid a runoff. He easily beat his top challenger, Chief Executive Abdullah Abdullah, who scored 39.52 percent.

Candidates now have three days to file any complaints they may have before final results are announced, probably within a few weeks.

As soon as results were announced, Abdullah's office said in a statement he would contest them.

"We would like to make it clear once again to our people, supporters, election commission and our international allies that our team will not accept the result of this fraudulent vote unless our legitimate demands are addressed," the statement read.

Abdullah lost to Ghani in 2014 in a divisive election that saw the US intervene to broker an awkward power-­sharing deal between the two rivals.

Preliminary results were originally due October 19 but were repeatedly delayed amid technical issues and allegations of fraud from various ­candidates, particularly Abdullah.