Barely had the last ballots been cast Saturday evening before the incumbent's spokesman declared: "Bongo will win... we are already on our way to a second mandate."
Bongo, 57, has been in power since a disputed election held in 2009 after the death of his father, Omar Bongo, who had ruled the oil-rich Central African country for 41 years.
Today, the campaign manager of Bongo's rival Jean Ping told reporters that the former head of the African Union Commission had won 60 per cent of votes counted so far, just under half of the total, against 38 per cent for the president.
"That's totally crazy," countered Bongo's spokesman. "It's tight, but we are ahead."
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Interior Minister Pacome Moubelet Boubeya has insisted that only results from the election commission cleared by his ministry had any validity.
Before polling began Boubeya said everything was "in place to guarantee a transparent and impartial election".
The results of the poll, which is decided by simple majority, should be declared at around 1600 GMT on Tuesday, Boubeya said in a later statement.
"More than ever we appeal for calm and recall that it is illegal to declare results before the relevant authorities do," added the minister.
But the acrimony that had marked the campaign period continued into the weekend with each of the main rivals accusing the other of mischief.
"We have observed massive fraud, in particular in areas where opposition representatives arrived in polling stations first," said Bongo's spokesman.
As he cast his own ballot Saturday morning, Ping told reporters, "We know the other side is trying to cheat. It is up to you to be vigilant."