* Provisional results give Biya 77 percent
* Opposition has asked for vote to be annulled
* Official results expected by Oct. 24
YAOUNDE, Oct 18 (Reuters) - Preliminary results for Cameroon's presidential election showed a widely expected landslide victory for incumbent Paul Biya, a member of the national vote counting commission told Reuters on Tuesday.
The results gave Biya 77 percent, well ahead of his main rival John Fru Ndi on 10 percent, said the commission member, who declined to be named because under Cameroon law only the Supreme Court can give the results.
Cameroonian media reported the same margin of victory for Biya, who has ruled the central African oil-producer for 29 years. The Supreme Court has until Oct. 24 to publish the validated results.
On Monday the opposition alleged irregularities in the Oct. 9 poll, saying it should be annulled and a fresh election called within six months.
Seven opposition candidates including the main Social Democratic Front of Fru Ndi, signed a joint declaration warning that if their demand was not met, their supporters would take to the streets in protest.
The ruling CPDM party issued a statement on Tuesday saying the opposition's declaration was provocative and unjustified.
Cameroon is the world's fifth largest cocoa producer and the region's breadbasket, supplying food to Chad, Central African Republic, Congo Republic and Gabon. It also hosts the Chad-Cameroon crude oil pipeline.
Its $ 22 billion economy is the region's biggest, making any unrest in the country, potentially damaging the region. (Reporting by Tansa Musa; Editing by Bate Felix and Mark John)