Voters and officials braving torrential rain to take part in Mali's presidential election run-off Sunday voiced concerns that the weather could badly affect turnout, in a vote seen as crucial to restoring stability in the conflict-scarred nation.

Residents in the capital Bamako woke up to gloomy skies and heavy downpours, and polling stations reported smaller numbers of voters than during the first round, when a turn-out of nearly 50 percent was seen as a key sign that the electoral process would be viewed as credible.

"At the moment, it's a disaster," said an election commission delegate at a voting centre in Bamako, telling AFP numbers were significantly down on the 300 people who had turned up by the same point in the July 28 vote.

"Today there are not even 20 and we really hope the rain will stop and people will come to vote," he said.

Polls opened at 8:00 am (0800 GMT) with former premier Ibrahim Boubacar Keita the favourite to win an election which will decide who leads Mali's recovery from a military coup last year, which led to an Islamist occupation of the north and a French military intervention.

Keita finished almost 20 percentage points ahead of runner-up Soumaila Cisse, an ex-finance minister, in the first round but failed to get an outright majority in a field of 27 candidates, propelling the two into Sunday's run-off.

"The rain is trying to ruin our day. I hope it stops, otherwise they will have to extend the voting hours," said Oumar Toure, one of the few voters who had turned up at a polling station set up in a city centre school.

Student Mariam Kante told AFP a large crowd had assembled at the centre by 8:00 am in the first round.

"The rain needs to let us fulfil our civic duty -- the future of Mali is at stake," she said.

Mali is in the middle of a season known as "wintering" which brings heavy rainstorms to the south of the country, where the majority of the population of more than 14 million live. Many observers had urged election organisers to delay the vote for better weather.

In Kati, a garrison town 15 kilometres (nine miles) from Bamako, Djibril Coulibaly, the chief official in a large high school told AFP no one had yet turned up to vote.

"Let's pray to God that the rain stops," he told AFP.

The road between Bamako and Kati was deluged in several sections, preventing the passage of vehicles, especially the numerous motorcycles heading to polling stations which were were forced to turn back.

But the rain did not seem to have deterred horse-racing punters who had gathered in large numbers outside a betting shop in Bamako.

"We don't really give a damn about the election. What we care about is feeding our families," said one of them.