A man with a knife has been arrested by police at Gare du Nord station in Paris.
A police official said that a man walked into the train station wielding a knife on Saturday and was immediately surrounded by heavily armed police.
Video online shows the police surrounding a man on the ground as travellers hurried past.
No-one was injured.
The Gare de Nord is one of the French capital's main transit hubs, serving the city's metro, suburban trains as well as intercity and high-speed trains like the Eurostar from London.
It comes amid heightened security after a policeman was killed and two others injured in Paris on Thursday night in an attack on the Champs Elysees.