Paris (CNN) A massive blaze at Notre Dame Cathedral in Paris devastated large parts of the 850-year-old church on Monday evening. Here's what we know so far.

How did the blaze unfold?

At 6:20 p.m. local time (12 p.m. ET) on Monday, a fire alarm rang out, interrupting mass. Security guards started to evacuate the cathedral even though they did not see any sign of a fire, a spokesman for the Paris fire brigade told CNN.

François-Xavier Lochet, a 70-year-old worshiper, said the congregation had just begun the Universal Prayer when the siren sounded. He said visitors were ushered out but those gathered for mass remained in place. Lochet said mass continued until a police officer went up and told the priest: "This is no joke. You've got to get out."

Twenty-three minutes later, at 6:43 p.m. (12:43 p.m. ET), a second alarm blared and the fire was visible at that point, the fire department said.

Around 400 firefighters were deployed to the scene but were delayed slightly by rush hour traffic.

Police in Paris confirmed a fire had taken hold at Notre Dame and asked the public to avoid the area in a tweet sent at 7:20 p.m. (1:20 p.m. ET). A minute later, Paris Mayor Anne Hidalgo posted a tweet saying "a terrible fire is underway" with photographs taken outside the church: one of smoke billowing from near the spire and over the towers, and a second showing the fire department responders working at the scene.

Shortly before 8 p.m. (2 p.m. ET), the cathedral's famed spire burned to a blackened shell before finally toppling, as thousands of Parisians who had gathered in the streets watched in horror.

Around 11 p.m. (5 p.m. ET), French President Emmanuel Macron announced: "The worst has been avoided. The façade and the two main towers did not collapse."

At 9:30 a.m. (3:30 a.m. ET) on Tuesday, French firefighters announced on Twitter that after nine hours of intense battle, the flames had finally been extinguished. Two policemen and a firefighter were injured, the tweet added.

2/2 Après plus de 9h de combats acharnés, près de 400 pompiers de Paris sont venus à bout de l'effroyable l'incendie. 2 policiers et un sapeur-pompier ont été légèrement blessés. pic.twitter.com/re9ZR0KB3W — Pompiers de Paris (@PompiersParis) April 16, 2019

Read More