Gabon's opposition presidential candidate Jean Ping has claimed victory over incumbent President Ali Bongo, whose family has ruled the oil-rich African nation for nearly half a century.

"As I speak to you, the trends indicate we're the winner of this important presidential election," Ping told supporters on Sunday at his campaign headquarters in the capital Libreville, according to Reuters news agency.

Ping, 73, made his declaration despite warnings by the country's interior minister against candidates giving results ahead of their official announcement on Tuesday. Ping also distributed figures that claimed to show him easily beating 57-year-old Bongo.

"I have been elected. I am waiting for the outgoing president to call to congratulate me," Ping said, according to the AFP news agency.

"You have foiled the congenital fraud of this regime which we are finally going to see off," he added.

Bongo said later on Sunday that he was "calmly" waiting for the results, while his campaign said they were confident he will hold on to power.

"We respect the law ... so we are waiting calmly for Cenap (the national election commission) to announce the results of the election," Bongo told a crowd of supporters, according to AFP.

Voters in Gabon head to polls as Bongo seeks second term

Official results from Saturday's vote are not due out until 1600 GMT on Tuesday and candidates are prohibited by law from making announcements on the likely outcome.

Igor Simard, Bongo’s spokesman, said that nobody could claim victory when votes were still being counted by the authorities.

"The fight is tight but we are confident our candidate will win," Simard told Al Jazeera.

"What gives us confidence is that the remaining constituencies to be declared are traditionally our strongholds," he said.

The head of the Pan-African Democracy Observatory, an NGO based in neighbouring Togo, downplayed the significance of Ping's declaration.

"We should not be surprised if one or the other declare victory. It's all part of the game," Djovi Gally told reporters.

Gabon's one-round electoral system means the winner simply requires more votes than any other candidate.

In 2009, Bongo won with 41.73 percent of the vote.

Ping and Bongo family ties

A former foreign minister and African Union Commission (AUC) chairman, Ping was a close ally of the incumbent president's father, Omar Bongo, who ruled for 42 years until his death in 2009.

Ping and the younger Bongo worked for years together under Bongo senior, who was responsible for getting the current opposition leader his job as chairman of the AUC.

Ping also has close family ties to the Bongo dynasty: he was formerly married to Omar Bongo's eldest daughter with whom he had two children.

But, Ping turned on Bongo junior in 2014, and in March he told French daily Le Monde that "Gabon is a pure and simple dictatorship in the hands of a family, a clan".

On Sunday, the streets of Libreville were almost deserted. Fearing a repeat of the violence that followed Bongo's contested victory in 2009, many residents, who had stocked up on food, stayed indoors. Shops and stalls usually open on Sundays were shuttered.

In the clashes that followed Bongo's 2009 victory, several people were killed, buildings were looted and the French consulate in Port Gentil, which saw the worst of the violence, was torched.

An oil producer with a population of less than two million, Gabon is one of Africa's richest countries.

However, declining oil output and falling prices have resulted in budget cuts and provided fodder for opposition claims that average people have struggled under Bongo's leadership.

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Source: Al Jazeera News and agencies