Police on Tuesday responded to an alert at Paris's Notre Dame Cathedral amid reports of gunshots and panic.
The assailant is reported to have been shot in the chest.
The area around the cathedral has been closed and police have asked people to stay away.More news: Shares in HD Supply Holdings Inc (HDS) Acquired by Clinton Group Inc
The motive for the attack is not yet known.
The attacker was wounded but not killed, police said.
CBS Radio News' Elaine Cobbe reports that the investigation has been handed over to the police's anti-terrorism unit. At least 600 people were blocked inside the iconic 12th century church while police first secured the streets around it, then combed the pews while visitors sat with their hands raised for the check. "The police didn't seem interested in him at the beginning", Metreau said.More news: Woman alleges gang rape in auto-rickshaw
People were evacuated from the tourist attraction around 3.45pm with reports flooding social media of shots being fired.
Paris police told CNN that a man was shot after attacking an officer with a hammer.
Paris remains under high security after a string of Islamic extremist attacks in recent years, including several targeting police officers and security personnel. Three months ago, another terrorist went on a spree that ended with an attack on security forces at Orly Airport in Paris.More news: Paris Police Shoot, Wound Hammer-Wielding Assailant Outside Notre Dame
Another police official said the attacker surged at police patrolling the scene with a hammer.
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