The Notre-Dame housed priceless artefacts and objects of huge cultural and historical significance before the devastating fire.
Paris mayor Anne Hidalgo confirmed several of the most sacred had been saved, while culture minister Franck Riester said others were being held under lock and key at the city hall.
Here are some of the famous objects and artworks associated with Notre-Dame:
Crown of Thorns
Purported to be a relic of the wreath of thorns placed on the head of Jesus Christ at his crucifixion, the hallowed object was stored in the cathedral's treasury.
French King Louis IX brought the relic, which is contained in an elaborate gold case, to Paris in 1238.
Ms Hidalgo said the Crown of Thorns had been taken into safekeeping.
Tunic of Saint Louis
The simple garment, said to have been worn by Louis IX as he brought the Crown of Thorns to Paris, was also kept at the cathedral.
Ms Hidalgo said it had been saved.
Among the most famous architectural features of the Gothic masterpiece, the stained glass rose windows are treasured artworks in their own right.
The three rose windows, which date back to the 13th century, adorn the north, south and west facades.
There were hopes the windows had escaped being destroyed by the fire after firefighters stopped its spread.
With nearly 8,000 pipes, some dating back to the 1700s, Notre Dame's master organ is one of the largest in the world.
The monumental instrument, the largest in France, was fully restored in 2013 with each pipe cleaned.
Paris' deputy mayor said the organ remains intact after the fire.
Emmanuel Gregoire told BFMTV that a plan to protect the cathedral's treasures had been rapidly and successfully activated.
The organ was constructed by Francois Thierry.
Housed in the two western towers, Notre-Dame's bells have rung out at key moments in France's history.
Emmanuel, the largest bell, was lifted into the south tower in 1685 and weighs over 23 tonnes.
Victor Hugo's Hunchback of Notre Dame, Quasimodo, was the cathedral's bell-ringer.
The fire was prevented from spreading to the bell towers.
This is what we know so far about the violent blaze:
Fire in the attic
The fire began around 5.50pm (Irish time) yesterday.
"I was not far away, I saw the smoke. At first I thought it was the Hotel-Dieu (hospital) but then I realised it was the cathedral. When I arrived, ash was beginning to fall," said Olivier De Chalus, head volunteer guide of the cathedral.
The cause of the blaze was not immediately known. It spread from the attic, and quickly across a large part of the roof.
The flames devoured the roof's wooden frame, which is more than 100 metres in length and nicknamed "the forest".
An investigation was opened for accidental destruction by fire, Paris prosecutors said.
Investigators were focused on whether the fire spread from the site of ongoing reconstruction work on the roof of the cathedral, a source close to the investigation said.
Construction workers were spoken to Monday evening by investigators, the department said.
Fire 'under control'
Firefighters announced early today the fire was "completely under control" and "partially extinguished". Only "residual fires" were still burning.
Around 10pm (Irish time), they announced that the structure of the cathedral had been "saved and preserved".
From the moment the fire was spotted, a major emergency operation was put in place to contain the blaze.
Four hundred firefighters with 18 fire hoses, some perched on cranes tens of metres off the ground, battled to contain the fire as quickly as possible.
However, using water-bombing aircraft - as suggested by US President Donald Trump - was not considered: "If used, (this) could lead to the collapse of the entire structure of the cathedral," France's civil security service tweeted.
Extent of damage
At around 6.50pm (Irish time), the cathedral's spire - one of Paris's most famous landmarks at 93 metres high -- collapsed.
Within a few hours, a large part of the roof had been reduced to ashes.
The extent of the damage inside the cathedral was not yet known by around 10pm Irish time.
"The fire affected two-thirds of the roof, which has collapsed, as well as the spire," said Paris fire brigade chief Jean-Claude Gallet, adding that the operation was focused on preserving the rear of the cathedral where the most valuable works are located.
The Holy Crown of Thorns and a sacred tunic worn by 13th-century French king Louis, two irreplaceable artefacts, had been rescued, the cathedral rector Patrick Chauvet said.
'Years of work'
Restoring the building will take "years of work", said the newly-elected president of the Bishops' Conference of France, Eric de Moulins-Beaufort.
In response to "multiple requests" the Fondation du patrimoine, a hertitage organisation, will today launch a "national collection" for the reconstruction of Notre-Dame, Anne Le Breton, deputy mayor of the French capital's 4th arrondissement, said in a statement to AFP.
Overnight the Pinault family, one of the richest in France, pledged €100 million for Notre-Dame.
French President Emmanuel Macron, who headed to the scene, said a "national undertaking" would be launched, and that "far beyond our borders, we will appeal to the greatest talents... who will contribute, and we will rebuild".