Cameroonian President Paul Biya is running for an eighth term on Sunday that could keep him in office until he is nearly 100, seeking to overcome frustration with his decades-long rule and a spirited challenge from a former government mouthpiece.

Biya took office in 1982 and has held a tight grip on power ever since, doing away with the presidential term limit in 2008 and winning re-election by comfortable margins.

His government has denied claims of ballot stuffing and manipulating the courts to sideline opponents.

Maurice Kamto, Biya's top challenger in the 2018 election, has been disqualified this time and the remaining contenders have failed to rally around a unity candidate, boosting the president's victory chances.

Biya rarely appears in public, fuelling consistent speculation that he is in poor health. The government last year banned public discussion of the topic.

He has attended one campaign rally this year, on Tuesday in the northern city of Maroua, where he thanked people for their support "despite the false omens, the slander, the fabrications".

He acknowledged complaints about basic services like roads and electricity in the cocoa and oil-producing country.

"I am well aware of the problems that are of concern to you. I am aware of the unfulfilled expectations that make you doubt the future," he said. "I can assure you that these problems are not impossible to overcome."

FORMER SPOKESPERSON BECOMES CHALLENGER

The challenger drawing the biggest crowds is Issa Tchiroma Bakary, a former government spokesperson who previously served as employment minister but announced in June that he was defecting.

Tchiroma has accused Biya of mismanaging Cameroon's resource wealth, leaving it dependent on international financial institutions.

"Their failure is everywhere," he said of the ruling party while campaigning. All Cameroonians are fed up with their management."

It is unclear whether the energy of Tchiroma's rallies will translate into votes.

"One is left with the impression that if this mobilisation is transferred into the ballot box then change is coming," said Pippie Hugues, a Cameroonian political analyst.

"However, the reverse might be true. We have seen such mobilisation in 2018, and nothing changed."

Raoul Sumo Tayo, senior researcher with the Pretoria-based Institute for Security Studies think tank, said Tchiroma might perform well in cities but would struggle in rural areas where the ruling party has a strong turnout operation fuelled by patronage.

"The ruling party is likely to be declared the winner of the election," he said. "Nevertheless, Tchiroma has demonstrated a strong ability to mobilise support to contest the results."

Twelve candidates are running in the election, and Cameroon does not hold run-offs, meaning the top vote-getter on Sunday wins.

Results must be announced within 15 days.