In this photo taken Monday Oct. 22 ,2018, supporters of Cameroon's Incumbent President Paul Biya, of the Cameroon People's Democratic Movement party, celebrate his election victory in Yaounde, Cameroon. Image Credit: AP

Douala: Cameroon police on Saturday arrested around 50 supporters of opposition figure Maurice Kamto during an unauthorised march in Douala, Kamto's spokesman said.

"Mass arrests of activists (Mrs Michele Ndoki and around 50 others) and of supporters demonstrating peacefully today," the spokesman, Olivier Bibou-Nissack, said in a Facebook post.

His boss, Kamto, has rejected the official outcome of this month's presidential election, in which he was one of seven candidates seeking to unseat President Paul Biya who has ruled Cameroon for 36 years.

In the end, Kamto came second with 14.23 per cent of the vote, against 71.28 per cent for Biya.

Michele Ndoki is one of his lawyers who protested before the Constitutional Council against what she called "massive and systematic fraud" during the election.

Bibou-Nissack said the headquarters of Kamto's party, Movement for the Rebirth of Cameroon (MRC), had been vandalised.

The building was cordoned off by police who stopped anyone from approaching, an AFP journalist said.

On Friday, government minister Paul Atanga Nji warned that "any attempts to disturb the public order will be met with the greatest firmness".

Cameroon authorities were not available for comment Saturday afternoon.