In September, three women were arrested after police found a auto loaded with gas cylinders abandoned near Notre Dame - with France's interior ministry saying it was likely to have been an imminent attack.
He was also found to be carrying kitchen knives and had a document identifying him as an Algerian student, the authenticity of which authorities were checking, Gerard Collomb told reporters.
"His colleague reacted with sang-froid and fired to ensure the attacked officer was not further injured", Collomb said.
Paris police say an unidentified assailant has attacked a police officer near the Notre Dame Cathedral, and the officer then shot and wounded the attacker.
The attacker was shot in the thorax and one officer had minor injuries.
The Paris prosecutor's office said the investigation was opened Tuesday soon after the attack.
France is under a state of emergency imposed after a series of terrorist attacks in 2015 and 2016, mostly claimed by the Islamic State extremist group, that left over 230 people dead.
"We're trapped in Notre-Dame de Paris, something is happening outside".
In the last fatal attack, a policeman was shot and killed on Paris's prestigious Champs-Elysees avenue on April 20, three days before the first round of the presidential election.
The episode began when the attacker "approached a police officer, took a hammer from his backpack and hit the police officer over the head", said a police spokesman, Yves Lefebvre.
Hundreds of people were in the cathedral when the incident unfolded. In the intervening months, there have been scattered incidents, most involving attacks on police and other security personnel.
Paris police said a "number of police" are at the square in front of the cathedral. "The police didn't seem interested in him at the beginning", Metreau said.
"People were extraordinarily calm, helping those who don't speak English translate", she said, adding that she felt safe but the situation was terrifying.
Witnesses around Notre Dame Cathedral are describing a dramatic police operation in the tourist-filled site in central Paris.
Authorities in Paris asked the public to stay away from the area.
One holidaymaker wrote on Twitter: "Not the holiday experience wanted".
In January 2015, two Islamist gunmen killed 17 people at the Paris office of satirical magazine Charlie Hebdo.