"I am the winner," opposition candidate Jean Ping declared on Sunday.
"I'm waiting for the president [Ali Bongo] to call and congratulate me," he told his supporters gathered at his headquarters in the Libreville capital.
On Monday he repeated the same message, insisting he had figures of preliminary results proving he had beaten Bongo 60-to-40 with 60 percent of the ballots counted.
The government has dismissed Ping's claims as being not only "dangerous" but "illegal".
Under Gabon's law candidates are not allowed to announce results before an official announcement, expected on Tuesday.
Ping says he declared himself the winner to prevent Bongo from "cheating".
But the president's camp argues that Bongo is poised to win a second term in office.
Two presidents for one country
"The fact that the two candidates are claiming victory is not surprising for us," Teophane Biyoghe, a law student told RFI by phone from Libreville.
"Jean Ping was very determined from the beginning. I also think that President Ali Bongo was also very determined. It was a very intense campaign and now the feeling that we all have here in Gabon is that the coming days are going to be even more intense."
Some voters have voiced concerns of a repeat of the violence that marred elections in 2009.
"We don't know if the opposition will accept the results if they don't go in favour of Jean Ping and we also don't think the presidential camp or the militants of Ali Bongo will accept the results if they don't go in favour of the president," added Biyoghe.
Two self-proclaimed presidents claiming one throne may be new for the oil-producing nation but not for the continent.
"Côte d'Ivoire was plunged into post-electoral crisis in 2010, when Alassane Outtara and Laurent Gbagbo both declared themselves winner," explains Kamissa Camara, a program manager at the Washington-based NGO National Endowment for Democracy.
"If both candidates [in Gabon] are already declaring themselves winners, it means that their respective supporters are already getting ready to celebrate a victory and, since there is only one presidential chair, I don't see how this could not go down into violence."
In 2009 clashes broke out in Gabon's oil-rich region of Port Gentil, where hundreds of people were forced to flee the city by boat.
Today many are stocking up on food and staying at home.
"People are barely walking in the streets," says Théophane. "The shops are closing very early at night, most of the time they close at 10.30 [pm], now they're closing at 7.00."
Earlier on Monday, the former chairman of the African Union held a press conference to reassure voters.
Ping, a former African Union chairman, also met the ambassadors of both France and the United States and reasserted his claim that only he can bring about meaningful change for the Gabonese people.
Product of the system
However as a former ally of Ali Bongo's father, Omar, Ping has not escaped criticism of collusion with the system. He even married Omar's daughter Pascaline, having two children with her.
"What's different this time is that he has a real willingness to break ties and he has the support of civil society," author Antoine Glaser told RFI by phone from Paris.
One of the things he's talked about revising is Gabon's relationship with France: That relationship has often been referred to as a cosy system of vested interests known as Françafrique.
Break with the past
During the Cold War French presidents supported corrupt African officials, in exchange for petrodollars and other benefits.
But Glaser, who has written a lot about this system, says privileged relations no longer define Paris's foreign policy towards its former colony.
"Gabon is less a priority for France now, it's more in west Africa, and even the French army in Gabon has diminished. You have 500 soldiers now, whereas in the past there were around 900," he says.
France's market share in Gabon has also fallen from 55 to 20 percent, as new countries like China, Morocco and Turkey gain traction.
"Things are changing a lot," insists Glaser.
"I think France is not as it was before under Omar Bongo who was not only Francophone but Francophile, he was very proud of his strong relations with the French presidents. But I think Ali Bongo, is a lot more different, he prefers to go to London than Paris!"