Police in Paris shot and wounded an attacker near the Notre Dame Cathedral after the perpetrator tried to hit them with a hammer. At the moment the motive for the attack is unknown, but clearly French authorities are taking no chances. They issued an alert to stay out of the area, and have flooded the area with police:

DEVELOPING: Paris police says police operation ongoing at Notre Dame Cathedral, urge people to avoid the area https://t.co/MiENa7bBsa pic.twitter.com/lW9wZehkru

— CBS News (@CBSNews) June 6, 2017

"Eyewitnesses say a man was shot by police as he tried to attack a police officer," CBS News' Elaine Cobb reports https://t.co/T5uqoA85rO pic.twitter.com/pvHBcC5UK5

— CBS News (@CBSNews) June 6, 2017

Paris police say a security operation is under way near Notre Dame Cathedral and are urging passers-by to stay away from the area.

The police department tweeted about the operation on Tuesday afternoon but did not provide any details. A police official would not provide further information.

French channel BFM TV reported that a policeman shot a man who tried to assault him. A police source told the Reuters news agency that the man approached the police officer with a hammer.

France has opened a terrorist investigation into the incident, but that’s pretty much standard operating procedure now in Europe after this kind of incident. France has stepped up its security around its monuments and other potential targets for terrorism, and have also seen “lone wolf” attacks on police at these locations before. Four months ago, police shot a machete-wielding, radical Islamist terrorist at the Louvre, but not before he injured a police officer. Three months ago, another terrorist went on a spree that ended with an attack on security forces at Orly Airport in Paris.

That doesn’t necessarily mean that today’s attack was terror-related, but French authorities want to err on the side of caution, and for good reason. So far, it appears they’ll be able to interrogate the attacker:

The attacker was wounded but not killed, police said.

Police earlier tweeted that they were responding to an incident at the square outside the cathedral and warned the public to stay away. BFMTV reported that hundreds of people were being held inside the cathedral.

Speaking of which, some tourists found themselves on lockdown inside the cathedral without any initial information as to what had happened:

We're trapped in Notre-Dame de Paris, something is happening outside. Police sirens can be heard. They are not letting anyone in or out

— Matthew Currie Holmes (MCH) (@mch2k) June 6, 2017

They may be there for a while, and it might not be the worst place in Paris to wait out the search for any potential accomplices. They will want to be sure that the hammer attack wasn’t a diversion for a more significant terror attack, but the length of time that has already passed suggests that it’s not part of another larger plot. We’ll update as more details become known.

Update: One policeman was wounded, but the situation is now considered under control:

UPDATE: Paris police say they are now in control of the situation at Notre Dame Cathedral https://t.co/GSKO4E2aXL pic.twitter.com/m3acsLrE3p

— CBS News (@CBSNews) June 6, 2017

The people in Notre Dame will be relieved to hear that.

Update: So the motive turned out to be … pretty much what everyone expected:

Notre Dame attacker shouted "this is for Syria" during assault on police officer, French interior minister says https://t.co/XcmpCtKs7f

— BBC Breaking News (@BBCBreaking) June 6, 2017

Quelle surprise! France has officially designated this a terrorist incident.