'This is for Syria': Man gunned down after attacking police with hammer at Notre Dame

A French policeman has shot a hammer-wielding attacker, who reportedly yelled “this is for Syria”, as he lunged at another officer outside the iconic Notre Dame cathedral in the heart of Paris on Tuesday afternoon.

Police sealed off the area in front of the cathedral, where the attacker lay injured on the ground.

The attack comes with France on high alert for more jihadist strikes after a weekend attack in London, where extremists used a van and knives to crush to death and kill seven people, one of them French.

"A man came behind these police officers and, armed with a hammer, started hitting one of them. His colleagues reacted with composure... and fired," Collomb told reporters near the cathedral in central Paris, following the incident on Tuesday.

While his identity has not been released, it is believed the man is a mature-aged student from Algeria.

A man was shot by police after he attacked an officer with a hammer outside Paris's Notre Dame Cathedral. Source: AP

: Notre Dame neighbourhood is surrounded by police after a man struck a police officer with a hammer. Source: Getty Images

Collomb added that the injured attacked was being treated in hospital and seemed to have acted alone.

Following the incident the Paris prosecutor's office swiftly launched a counter-terrorism investigation.

Armed police cordoned off the site and the cathedral in central Paris that is visited by millions of tourists every year was locked down during the incident.

It comes just three days after Islamist militants killed seven people in London in a knife and van attack.

"Situation under control, one policeman injured, the assailant was neutralised and taken to hospital," Paris police said on Twitter.

Two police sources said the officers shot the assailant in the thorax after he had threatened them with a hammer and refused to stop. One policeman was hurt, according to one source.

Much of the iconic city was placed into lockdown following the attack. Source: Getty Images

Armed police cordoned off the site and the cathedral in central Paris that is visited by millions of tourists every year was locked down during the incident. Source: Getty Images

Karine Dalle, a spokeswoman for the Paris diocese, told BFM TV 900 people were inside the cathedral as police secured the area.

One 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 under a state of emergency after a wave of militant attacks since early 2015 have killed more than 230 people across the country.

Three women were arrested in September after police found a car laden with gas cylinders abandoned near Notre Dame cathedral in what the interior ministry at the time said was a likely planned imminent attack.