Vote counting is under way in Cameroon following Sunday's presidential election in which incumbent Paul Biya is seeking to extend his 43 years in power.

Biya, who at 92 is the world's oldest head of state, is being challenged by nine candidates. If he wins, it will be his eighth consecutive term in office, with the next election due in 2032.

Interior Minister Paul Atanga Nji said that voting took place "hitch-free" across the country. But there was a call for a boycott in the English-speaking regions in the west and there were reports of clashes in the north.

The final result should be known within 15 days of the vote.

In the run-up to the election there were complaints from the opposition of attempts to suppress their support.

In August, the Constitutional Council barred 71-year old Maurice Kamto, widely viewed as the main challenger, from taking part.

On Sunday, angry supporters of leading opposition candidate and former Biya ally, Issa Tchiroma Bakary, 76, took to the streets in his stronghold of Garoua. They clashed with security forces, who fired tear gas, after his residence was cordoned off.

Earlier in the day, Tchiroma had said he was the subject of threats.

"It is not Tchiroma who is the problem, he told reporters, adding that he "places himself under the protection of God and the Cameroonian people."

"I am at home; I will not move. If they intend to come and take me away from home, I will not move," he declared.

Despite this Interior Minister Nji said the polls were held without major incidents in all 10 regions of the country.

He did not comment on the situation in Garoua but rather repeated previous claims that some presidential candidates were planning to publish the results of the election ahead of the official declaration.

Nji described this as a major red line, threatening action against anyone suspected of breaking the law.

In the two restive Anglophone regions, where separatists attempted to bar residents from voting, some did turn out at the polling stations. But many others stayed away for fear of reprisals.