Andre Mba Obame could be boosted by the ethnic vote
Two days before elections in Gabon to replace the late President Omar Bongo, at least five out of 23 candidates have said they are pulling out of the race.
They say they will now back Andre Mba Obame, a former government minister.
But several other candidates denied media reports that they had also withdrawn in favour of Mr Obame.
The favourite to win Sunday's poll is Ali Ben Bongo, the son of the former president who ruled Gabon from 1967 until his death in June.
Some of the candidates have complained of voter registration irregularities, including Bruno Ben Moubamba, who has gone on hunger strike in protest.
He, however, denied reports that he was one of those who had withdrawn from the race and was supporting Mr Obame.
Following overnight talks, one of those pulling out of the race, Anna Claudine Assayi Ayo, said that "consultations resulted in a secret vote and the designation of Andre Mba Obame [as candidate]".
Mr Obame was the interior minister under President Bongo.
He was a senior member of the ruling Gabonese Democratic party (PDG) until deciding to run as an independent after it selected Ali Ben Bongo as its candidate.
He, and some of those who withdrew from the election, are from the Fang ethnic group - Gabon's largest - and correspondents say this could help him pose a serious challenge to Mr Bongo.
However, the anti-Bongo vote still looks set to be divided, while the PDG candidate enjoys the advantage of having the best-financed campaign.
Gabon is a major oil producer but most of its 1.4 million people live in poverty.
The late President Bongo was facing charges of corruption in a French court when he died.