Police and soldiers were deployed at strategic points in the city and traffic was light after Sunday's poll, pitting Andre Mba Obame and Pierre Mamboundou against Ali Bongo, the son of late ruler Omar Bongo Ondimba.
Bongo, the former defence minister, is widely tipped to win when official results are announced, which is likely to be on Wednesday evening, according to electoral officials.
But his principal rivals have both claimed victory.
The central African country was ruled by Omar Bongo for 41 years until his death in June, and 23 candidates initially came forward to replace him, but half a dozen withdrew before the race.
Both Mamboundou and Mba Obama announced precautions to protect their own figures from polling stations.
At Awendje in northeast Libreville, about 100 activists formed a security picket around the headquarters of Mamboundou's Union of the Gabonese People (UPG).
"We've been obliged to take measures. It's necessary that the reports (from polling stations) remain secure. We're sleeping here," said Aime Nzamba, a top official in the UPG.
Mba Obame's supporters did the same at his home in the northwest of the city, putting up tents around the house. Each politician has said they fear that the electoral commission and the interior ministry will falsify the results in Bongo's favour.
During the night, Mba Obame's supporters claimed that he had won with 50.1 percent of the votes, while Mamboundou had said on Monday that he was the winner, with 39.13 percent.
Ali Bongo's camp issued no figures and the campaign team, which includes many French citizens, opted for discretion, just claiming that their candidate had an absolute majority.
"People are frightened and prefer to stay at home," a taxi driver said on the streets of the capital, which were nearly as empty as on Monday, when many shops and offices remained closed. "It's very calm."
No official figures have been released by the electoral commission, which has been collecting results from across the nine provinces and said the winner will be announced between 6:00 pm (1700 GMT) and midnight on Wednesday.
Gabon has long been dominated by the Gabonese Democratic Party (PDG), which largely swung its weight behind Ali Bongo in the campaign and is built into the fabric of society.
The PDG is also widely accused of maintaining a system of favouritism in the country of 1.5 million, where more than half the population live below the poverty line in spite of the oil income and revenue from manganese and timber.
Mba Obame, former interior minister, said the build-up of troops around the capital was unwarranted.
"It looks like a coup," he told journalists.
"What could justify security forces when everyone, including France, recognises that the election took place under good conditions? Nothing. This is provocation," he added.
Each of the candidates has campaigned on a platform of redistributing the wealth. France, which has made a point of stating that it backs no particular candidate, added its weight Tuesday to the need for a share-out.
"It is now necessary to launch more socio-economic programmes and redistribute wealth in the fairest possible manner," France's Minister for Development Alain Joyandet told Le Parisien newspaper.
"The new president will have to fulfill a mandate that is a clear break from the past."
AFP
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