PARIS -- Police in Paris shot and injured a man who attacked an officer with a hammer at Notre Dame cathedral in the center of the city.
The attacker pulled the hammer from his backpack and attacked a police officer on duty outside the cathedral, police union spokesman Yves Lefebvre from the told BFM TV. He was shot in the chest by another officer.
Video posed on social media from the scene shows what appears to be the attacker laying motionless on the ground next to an officer outside the cathedral.
The attacker was wounded and taken to hospital, and the situation brought under control, police told CNN.
The incident caused panic among visitors in the area. France is still in a state of emergency following the Paris attacks in November 2015, in which 130 people were killed. There has been strong police presence on the streets of the capital city since then.
Notre-Dame cathedral is one of the most popular tourist attractions in Paris, and visitors typically line up in long queues to enter the building.
Hundreds of people were held inside the cathedral and photos on social media showed crowds inside with their hands in the air.
The Paris prosecutor's office said it had opened an anti-terror probe into the incident. Police on Twitter warned the public to stay away from the cathedral.
Kyle Riches, a tourist from San Francisco, was with his wife walking through the plaza outside Notre-Dame when they heard gunshots and dropped to the ground.
"My wife and I ran. We were trying to figure out what was going on," he said.
"We saw SWAT teams coming in to clear the area and started running."
He said that he and his wife saw police holding their guns up as they ran towards someone.
A woman in the area at the time of the incident said that she heard two shots.
"Everyone started fleeing from the cathedral and police surrounded almost immediately. It looked as though they had surrounded someone at the stairs down to the Seine (River)," said the woman, who gave her name as Abigail M.
"There was a large crowd in line to go into the cathedral and when the shots fired they all started running."
She said that police had sectioned off an area around the cathedral and down the street.
"We took cover in a nearby store and they left us there for about 15 minutes before fully clearing the area. I saw emergency services, military personnel and what appeared to be police dressed in bomb squad gear."
CNN's Angela Dewan wrote from London. Richard A. Greene and Joseph Netto contributed to this report.