Voting yesterday seemed largely quiet in the capital, but it was impossible to get information from the rest of the country after the government shut down communications during the polls.
Interior Minister Raymond Mboulou ordered telecoms firms to block all telephone, Internet and SMS services for 48 hours due to "reasons of security and national safety".
In what appeared to be an isolated incident, police fired tear gas to disperse a crowd of around 200 opposition supporters at a polling station in Brazzaville.
Polls closed at 1700 GMT and results are expected from tomorrow.
Also Read
"Things are going calmly," said Eric Katolo, head of an 18-person observer mission from the International Conference on the Great Lakes Region (ICGLR), before voting ended.
In Brazzaville's northern Ouenze neighbourhood, where support for the president is high, locals earlier said they wanted "stability" and "peace", two watchwords of Sassou Nguesso's re-election campaign.
"We don't want what happened in Libya to happen in Congo," said 29-year-old Papin, referring to the descent into chaos in the North African country after the 2011 ouster of longtime dictator Moamer Kadhafi.
In Poto-Poto, dozens of youths took advantage of a traffic ban to play football in the street in the city centre. There was a visible police presence, notably at checkpoints monitoring vehicles allowed on the road.
In the run-down Makelekele district in the south of the capital, few hid their opposition to the incumbent president. "He won't get 10 votes here," said Raymond, a 56-year-old builder.