The visitors were trapped in the pews after a hammer-wielding man, claiming to be a "soldier" of the Islamic State group, was shot and wounded just outside the church when he attacked a police officer.
While many of the some 1,500 people had come from around the world to see the church's famed stained glass and gargoyles, they instead found themselves instructed to keep their hands up while authorities searched for weapons.
"A voice asked us to be quiet in French, English and Spanish," said 42-year-old American tourist Nick, on a five-day visit to Paris with his wife.
She leaned against him, still shaken, as they walked out of the church once it was all over, saying "I'm scared, I'm scared".
Notre Dame, which is situated on the banks of the Seine river in the heart of Paris, draws 13 million visitors a year.
At around 4:20 pm (1420 GMT) the American couple had been waiting in line to enter when the attack kicked off. There was a commotion, then people began to run and then came two or three gunshots.
'Very scary'
"We heard that it was a man with a hammer. We hope he's a fool, not a terrorist," said Nick, who didn't provide his full name.
From his office on the second floor of presbytery, Notre Dame communications manager Andre Finot realised something was wrong when he heard the policeman's first shot.
"I saw three officers surrounding a man. A second shot rang out and the man fell to the ground," Finot said.
The officer was lightly wounded and the attacker was rushed to hospital after being struck by police gunfire.
Tuesday's incident comes three days after extremists used a van and knives to crush to death and kill seven people enjoying a night out in London. One of the victims was French.
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.
In the chaos of the moment on Tuesday it was not immediately clear what was happening and how serious the threat was.
"Suddenly they closed the doors. I was scared, I thought it was a bomb," said Juan, a Mexican in his 50s. "But thank God we were quickly told it wasn't and we were fine."
Once the doors were opened and the tourists were allowed to leave, many wasted no time in leaving the area. Some still had tears in their eyes as they walked out of the church's ornately carved stone entrance.
For some the security scare was enough of a shock to make them reconsider their plans in the French capital.
Alberto Loor, a 34-year-old Ecuadorian and Maria-Jose Di Mora, 28, were wrapping up their honeymoon in Europe. After the attack they decided to shorten their stay in Paris, without even a visit to the Eiffel Tower.
"It's very scary, we've never lived something like this", she said. "You feel a threat for your life".
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
