A man armed with a knife and a hammer wounded three people Saturday in an early morning attack at the bustling Gare de Lyon train station in Paris, another nerve-rattling security incident in the Olympics host city before the Summer Games open in six months.

The 31-year-old man, carrying residency papers from Italy and medicines suggesting he was undergoing treatment, was quickly taken into police custody following the attack at 7.35am in one of the station’s cavernous halls, authorities said. Millions of passengers ride the hub’s high-speed and commuter trains.

“This individual appears to suffer from psychiatric troubles,” said Laurent Nunez, the Paris police chief who is also in charge of the massive security operation for the July 26-August 11 Olympic Games.

While stressing that the police investigation was still in early stages, Nunez said: “There are no elements that lead us to think that this could be a terrorist act.”

A man was seriously wounded in the stomach and underwent surgery and two other people were more lightly hurt, authorities said.

Police investigators work inside the Gare de Lyon station. Photo / AP

Passersby helped railway police officers detain the suspect, Nunez said. He said the man was carrying residency papers delivered in Italy, allowing him to travel legally to other European countries.

The Paris prosecutor’s office said the man is thought to be from Mali in northwest Africa and that the police investigation is looking at a potential preliminary charge of attempted murder.

Posting on social media, Interior Minister Gerald Darmanin described the attack as an “unbearable act.”

Security in Paris is being tightened as it prepares to welcome 10,500 Olympians and millions of visitors for the first Olympic Games in a century in the French capital.

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The Games are a major security challenge for the city that has been repeatedly hit by Islamic extremist attacks, most notably in 2015, when gunmen and bombers killed 147 people in waves of assaults in January and November.

Soldiers patrol inside the Gare de Lyon station after an attack. Photo / AP

Most recently, a suspect targeted passersby near the Eiffel Tower in December, killing a German-Filipino tourist with a knife and injuring two others. The man was under surveillance for suspected Islamic radicalisation and had previously been convicted and served time for a planned attack that never took place.

Security concerns are particularly sharp for the Games’ opening ceremony along the River Seine. Tens of thousands of police officers and soldiers will be deployed to secure the Games’ first opening ceremony to be held outside the more easily secured confines of a stadium. Organisers recently downsized the planned number of spectators to about 300,000 from the 600,000 they’d initially mentioned.

Soldiers who patrolled the train station quickly helped restore a sense of calm and settle passengers’ nerves.

“Unfortunately one gets used to these kind of happenings around the world,” said Celine Erades, a 47-year-old at the station with her daughter. “We have very few cases like this, but it’s always deplorable when they happen.”