Collomb said he launched himself onto an officer, striking him with a hammer. A man who attacked a policeman with a hammer, who police subsequently shot and injured, pledged allegiance to ISIS before the assault.
Hundreds were holed up inside the cathedral, and photos on social media showed people with their hands in the air.
A witness in a flat overlooking the site told BFM TV the attacker could be seen lying motionless on the ground.
The cathedral, a Gothic landmark on the Ile de la Cite on the Seine, across from the headquarters of the Paris police prefecture, was sealed off, and about 900 visitors and worshippers were told not to leave until the situation was declared safe.
A police officer was killed on April 20 on Paris' Champs-Elysees avenue, another prestigious location visited by tourists.
One of the world's most famous Cathedrals was placed into lockdown after a man armed with a hammer attacked a police officer who was guarding the Notre Dame.
Lawrence Langner, a 73-year-old American, said he suddenly heard a commotion and two detonations like gunshots.
Police and gendarmes at the scene on Tuesday.
Authorities had asked people to stay away from the area and some took refuge inside the cathedral.
French prosecutors have reportedly confirmed a counter-terrorism investigation is underway following the incident.
Journalist David Metreau, who said his office overlooks the square that fronts Notre Dame, tweeted that there were two blasts that sounded like shots.
France is still under the state of emergency imposed after the November 2015 attacks in Paris, when Islamic State jihadists killed 130 people in a night of carnage at venues across the city. The attacker was shot dead by police. A police official would not provide further information.
Newly-elected President Emmanuel Macron, portrayed by rivals as weak on security during the presidential campaign, last month instructed the task force be created to bring together France's multiple security agencies inside the Elysee presidential palace.
In February, a 29-year-old man armed with two large knives and shouting "God is great" in Arabic lunged at a military patrol near an entrance to the Louvre in Paris and slashed a soldier.