Mauritania's President Mohamed Ould Ghazouani opened an early lead as vote counting was underway after Saturday's presidential election, provisional results from the country's electoral commission showed.

Ghazouani was leading with 49%, while his main rival, prominent anti-slavery activist Biram Dah Abeid, was at 22.68%, with around 6.49% of total votes counted, or 283 polling stations reporting out of 4,503 by 0010 GMT.

Ghazouani, 67, a former top soldier who is widely expected to win, has pledged to boost investment to spur a commodities boom in the West African country of 5 million people, as it prepares to start producing natural gas.

"The last word belongs to the Mauritanian voters. I commit myself to respecting their choice," Ghazouani said after he voted in the capital early on Saturday.

Elected for a first term in 2019, Ghazouani is facing a field of six opponents, among them Abeid, who came second in 2019 with over 18% of the vote.

Other challengers include lawyer Id Mohameden M'Bareck, economist Mohamed Lemine El Mourtaji El Wafi, and Hamadi Sidi El Mokhtar of the Islamist Tewassoul party.

Casting his ballot soon after polls opened in the capital Nouakchott, 39-year-old geographer Mohamed Cheikh Hadrami said he had voted for a candidate "who will be able to reconcile Mauritanians". He declined to say who he had voted for.

Some 2 million people were registered to vote, with major election issues including fighting corruption and creating jobs for the young.

If re-elected, Ghazouani has promised a natural gas-fired power plant from the Greater Tortue Ahmeyin offshore gas project, which is on track to start production by the end of the year. He has also pledged to invest in renewable energy and expand gold, uranium and iron-ore mining.

Ghazouani has presided with relative stability since 2019, while Mauritania's Sahel neighbours, including Mali, struggle with Islamist insurgencies that have led to military coups.

Mauritania has not recorded a militant attack on its soil in recent years and Ghazouani, who chairs the African Union, has promised to manage Islamist threats.

Abeid is challenging Ghazouani on his human rights record and the marginalisation of Mauritania's Black African population, while El Mokhtar has a following among conservative and religious voters.

"President Ghazouani will likely win the vote in the first round," said Mucahid Durmaz, senior West Africa analyst at risk intelligence company Verisk Maplecroft.

"The president's re-election bid has been boosted by the ruling party's landslide victory in legislative elections last year," he added.

If no candidate receives more than 50% of the vote, the election will go to a second round.

In the last election, some opposition candidates questioned the credibility of the vote, sparking small-scale protests.

"Everything indicates that people want change. I will have no problem recognising the results of a transparent election, but in case of fraud we'll not hesitate to call it a rigged election," El Mokhtar said after voting.

El Mokhtar was third with 14.42% of the vote, according to the provisional results on Saturday.