Dozens of police officers converged on a street in central Paris on Tuesday after an armed man took hostages, police sources said.
The man was "armed and holding at least two people," a source told AFP, adding that "the situation is quite confused", but did not appear to be terrorism-related.
"Based on our initial investigations it could be a mentally unstable person whose motivations are still unclear," another source said.
A spokesman for France's BRI intervention brigade said negotiations with the man were underway.
The standoff began around 4:00 pm (1400 GMT), with BFM television reporting that the man had entered the offices of a start-up company on the Rue des Petites Ecuries, a gritty area of the bustling 10th arrondissement.
At least one man was lightly injured while fighting with the hostage-taker and escaping before the BRI officers arrived on the scene, a police source said.
Crowds of bystanders were held back by a security perimeter at the site, where police and rescue workers were massed, deploying at least one remote-controlled robot on tracks toward the building where the armed man had barricaded himself.
France has been on high alert after a series of jihadist attacks in the past three years, most recently a Saturday night knife attack in Paris last month in which one person was killed.