YAOUNDE - Machete-wielding attackers beat a Cameroon opposition faction leader to death, gouged his eyes out and left his body in the street on Friday as an opposition power struggle spilled over into violence, witnesses said.

The attack came as rival conventions of the main opposition Social Democratic Front (SDF) were due to start, demonstrating a deep rift in a party that presents the biggest challenge to President Paul Biya, one of Africa's longest serving leaders.

The dead man was Gregoire Diboule, the party's provincial administrative secretary in the capital Yaounde, who had backed a challenge to longstanding SDF leader John Fru Ndi by senior party figure Clement Ngwasiri.

Ngwasiri, chairman of the party's national advisory council, had organised a breakaway party convention to start in Yaounde on Friday - the same day the main party convention was due to start 280km away in Bamenda.

"When I came back this morning I found some damage had been caused and the administrative secretary was killed and his eyes plucked off (gouged out)," local party official Victor Lembi told Reuters. Eleven other party members were injured, he said.

Lembi said there had been around 100 attackers, whom he said were supporters of John Fru Ndi.

Local residents said attackers had beaten Diboule with sticks and machetes and gouged his eyes out before leaving him in the street some 400 metres from the provincial party offices, where they smashed down doors and ransacked offices.

A Reuters reporter who arrived at the scene afterwards said police had sealed off the offices as well as a conference centre where the breakaway party convention was to have been held.

Witnesses said Diboule's body had been taken to a mortuary.

Police declined to comment. SDF leader Fru Ndi could not be reached in Bamenda.