Cameroon's President Paul Biya was re-elected to an eighth term with 53.66% of the vote, official results showed on Monday, raising the prospect of confrontations with supporters of the main opposition candidate who has claimed victory.

After the results were announced by the Constitutional Council, opposition challenger Issa Tchiroma Bakary wrote on Facebook that gunfire was being directed at civilians gathered outside his home in the northern city of Garoua.

Reuters could not independently verify his account and there was no immediate comment on his statement from the government.

Opposition protesters have clashed with security forces over the past week after partial results reported by local media showed Biya was on course to win the October 12 vote. The government rejected opposition accusations of irregularities.

Biya, 92, 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 reelection by comfortable margins.

He is the world's longest-serving ruler and a new seven-year-term could keep him in power until he is nearly 100.

"Hereby declared elected President of the Republic, having obtained the majority of the votes cast, the candidate, Biya, Paul," Clement Atangana, president of the Constitutional Council, said.

Tchiroma is a former government spokesperson and employment minister in his late 70s who broke ranks with Biya earlier this year.

He mounted a campaign that drew large crowds and endorsements from a coalition of opposition parties and civic groups. Last week he said he had won the election and would not accept any other result.