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A hammer-wielding man was shot town after attacking a police officer outside Notre Dame Cathedral in a suspected terror incident.

Armed officers swarmed the area and warned the public to stay away after reports of gunshots and panic outside the central Paris landmark.

Police confirmed the suspect was "neutralised" and local news sites were reporting that he was injured, but not killed, in the shooting.

French authorities confirmed the country's counter-terrorism office has launched an investigation into the incident, which left one police officer injured.

It is not yet clear if the attacker was acting alone when he attacked the police officer who had been patrolling in the Thorax.

According to Reuters, he threatened officers with a hammer and refused to stop when instructed, before officers opened fire.

Up to 900 tourists were locked inside the cathedral for their own safety as the incident unfolded.

A police source confirmed: "The area is in lock down, but the assailant has been neutralised."

They later added: "Situation under control, one policeman injured, the assailant was neutralised and taken to hospital."

One eyewitness said he and his family were among the people trapped inside Notre Dame after officers locked all the doors.

He wrote: "Me and my family are stuck in the church. Quick note. Everyone inside the church is safe. Whatever was happening happened outside."

He shared pictures of tourists standing with their hands over their heads at the request of police.

Referring to the UK terror attack over the weekend, he added: "Needless to say my family and I are a little on edge. We were in London when London Bridge attacks happened."

Another holidaymaker inside Notre Dame wrote on Twitter: "Not the holiday experience wanted. Trapped in Notre Dame Cathedral after police shoot a man. We are with our 2 terrified children."

France is currently under a state of emergency following a series of lethal attacks by Islamic State and al-Qaeda operatives.

This story is being updated.