Fifty-two baboons escaped on Friday from their enclosure at the Paris zoological park in Vincennes, on the southeastern outskirts of the French capital, according to reports.
The zoo has been evacuated, police have arrived and three marksmen armed with hypodermic guns are at the scene, the Daily Telegraph reports.
The latest reports suggest that all but four have now returned to their enclosure after being caught "in a net", according to police sources.
"Our colleagues have them surrounded," one policemen told Le Parisien. Zookeepers and vets were swiftly called in to round them up. "They can be dangerous. They mustn't get out of the park," said the police source.
A security perimeter has been established around the zoo to stop cars from driving in nearby roads.
The baboons escaped early this afternoon for unknown reasons but were "never in contact with the public" and gathered around a large rock in the centre of the zoo. "The situation is under control," said the Paris zoo in a statement.
The baboons bid for freedom first came to zookeepers' attention when they were spotted in a service corridor used by zoo staff. "Since then they were returned to their enclosure barring four of them that have been spotted in this service area and are in the process of being caught," said the zoo.
"As a precaution", the entire zoo was evacuated and is expected to remain shut until Saturday.
Paris zoological park underwent a total overhaul between 2008 and 2014, and was feted as being far more respectful of animals and the environment when it re-opened four years ago.