The BBC says officials have told people to stay away from the area; according to The Telegraph, the main square near Paris’ tourist attraction has been evacuated. David Rahul Metreaum, a witness, told BFMTV that he saw a “man on the ground who is not moving.”
Police swarmed the area and are circling the surroundings to make sure there are no accomplices. According to The Guardian, the French prosecutors office said that the counter-terrorism office is launching an investigation.
Paris is under high security after a series of coordinated terrorist attacks occurred in November 2015. Three suicide bombers struck during a football match while gunmen carried out a mass shooting at an Eagles of Death Metal concert in the Bataclan theatre. 130 were killed, and more than 350 were injured.
France has been on high alert since the January 2015 attacks on the Charlie Hebdo offices and a Jewish supermarket which killed 17.
The incident at Notre Dame comes just three days after a terror attack in London, which ISIS has since claimed responsibility for. Police in the U.K. arrested 12 suspects in response to the attack, which claimed at least seven lives and injured more than 40 others on Saturday night.