Alix Culberston, Express, June 6, 2017
Police confirmed they are attending an incident at the cathedral and have warned the public to stay away.
Tourists and worshippers were seen at 4.30pm local time (3.30pm BST) running away from the scene in the centre of the French capital while those inside were on lock-down.
Police shot a man who attempted to attack multiple officers with a hammer outside the popular tourist destination visited by million every year.
French interior minister Gerard Collomb, said the attacker shouted: “This is for Syria.”
In custody, he has told police he is “a soldier of the Caliphate”.
Counter terror officers have been called in to investigate the incident, they confirmed.
Paris Police’s SGP Unit confirmed one of their officers was “slightly wounded in the head by a hammer blow” and was taken to hospital.
The attacker is still alive and was being held on the ground by police after being shot in the thorax because he refused to stop.
He is now in hospital, police confirmed.
Visitors inside the cathedral have tweeted their families saying they are trapped inside the building.
One of those trapped was Nancy Soderberg, former White House Deputy National Security Advisor.
She had been with her niece, Fraser, in London on Sunday, the day after the London Bridge terror attack.
About a couple of thousand of people are inside, crouching down between the pews, a British witness said.
Police told everybody in the cathedral to raise their arms to show they were not armed.
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.”
The streets surrounding Notre Dame have been cleared by police.
A witness outside the cathedral, said: “I heard two explosions.”
Paris police, tweeted: “A police intervention is in progress in the square in front of Our Lady Intervention, avoid the area.”
British tourist, Matthew Currie Holmes, wrote on Twitter: “So we are trapped in Notre Dame Cathedral. Something is happening outside we don’t know what it is. Police sirens can be heard #NotreDame.
“Needless to say my family and I are a little on edge. We were in London when the London Bridge attacks happened.”
Matthew said police were asking everyone inside the Cathedral to raise their arms, suggesting they were looking for other armed assailants.
The motive for the attack was not immediately known.
Last September three women were arrested 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.
France has been in a state of emergency since the January 2015 attacks on the Charlie Hebdo offices and a Jewish supermarket in Paris which killed 17 people and wounded 22.
Since then soldiers have been patrolling streets alongisde police to protect tourist sites, government buildings and events.
In November 2015 during a series of coordinated terror attacks 130 people were killed by seven attackers.
Three suicide bombers struck outside the Stade de France during a football match.
There were then several mass shootings and a suicide bombing at cafes and restaurants.
Gunmen carried out another mass shooting and took hostages at an Eagles of Death Metal concert in the Bataclan theatre, killing 89 people.
The attackers then blew themselves up or were shot by police during a stand-off.
Another 368 people were injured, almost 100 seriously.