Voters in Gabon were called to the polls on Saturday for a triple election in which President Ali Bongo Ondimba, a descendant of a family that has ruled for 55 years, is seeking victory over a belatedly-united opposition.

Bongo and main rival Albert Ondo Ossa lead a race of 14 candidates competing for office in the small oil-rich central African state.

The 64-year-old incumbent is seeking a third term after taking office in 2009, succeeding his father Omar, who died after more than 41 years in power.

But as polling day became closer, an alleged conversation between Ondo Ossa and a fellow opposition figure took over the scene.

The conversation -- recorded without the pair's knowledge and spread on social media -- refers to various strategies "to create a power struggle" and gain support from other countries.

Bongo has accused the pair of treason, saying the remarks reflect a plot to take over with the help of "foreign powers."

At an eve-of-election rally attended by tens of thousands of supporters in Libreville, Bongo charged that the two sought to "destroy this country."

"We won't let them do it."

Onda Ossa, a 69-year-old economics professor who served as a minister under Bongo from 2006 to 2009, was chosen by the main opposition grouping, Alternance 2023, as its joint candidate just eight days before the election.

Alternance 2023 this week issued a statement strongly denying the "veracity and authenticity of this conversation" and accused the government of "shameful manipulation".

In the buildup to the elections, Bongo campaigned on increased family benefits and lower public school tuition. His adversaries, however, claim that in his 14 years as president, he has done nothing to distribute the country's oil wealth to its citizens.

Gabon, being one of Africa's leading oil producers, has a greater GDP per capita than many other Sub-Saharan African countries. Despite this, more than a third of its 2.4 million residents are poor, and unemployment levels reached 37%.

Bongo struggled in the shadow of his father. In 2016, he was narrowly re-elected with just 5,500 more votes than his rival, who claimed the election had been fixed.

During his 41-year reign, his father, Omar Bongo, became known for exploiting his country's natural riches to accumulate a fortune that comprised 40 luxurious houses in France, 66 bank accounts, and over 180 automobiles, including a $1.5 million (€1.38 million) Bugatti.

The announcement of the results sparked violence in the capital Libreville that left five dead, according to the government. The opposition says 30 people were shot dead by the security forces.

In October 2018, Bongo suffered a stroke that sidelined him for 10 months. His prolonged absence raised concerns that he was unfit to rule effectively and fuelled an attempted coup.

In recent months, he has been busy with foreign trips and a nationwide tour to defend his record.

In addition to voting for a president, Gabon's 850,000 voters will be choosing candidates for the legislature and local councils.

In the days leading up to the ballots, the main opposition parties have complained over a last-minute change to voting rules in the legislative race, which they say violates the separation of powers.

The new move stipulates that any vote for a local deputy will automatically be a vote for that deputy's presidential candidate.

Critics said the move would lead to an "unfair vote", favoring the ruling Gabonese Democratic Party (PDG) since Ondo Ossa is not backed by any single party.

Ondo Ossa has told AFP that if elected, he "will dissolve parliament and convene new elections" for the body.

The PDG has an overwhelming majority in the outgoing National Assembly. The protest over the voting rules followed another controversy five months ago. A change was introduced that abolished the need for a runoff if the first round fails to produce a winner with more than 50% of the vote.