The inferno broke out around 6.30pm local time (5.30pm BST). The fire was declared under control nine hours after it started, and fully extinguished around 10am (9am BST) on Tuesday morning. Officials said the cause could be linked to extensive renovation works underway, but this has not been confirmed.
The Paris prosecutor’s office said it was currently being investigated as an accident.
A firefighter and two policemen were slightly injured while tackling the blaze.
Firefighters managed to save the 850-year-old Gothic building’s main stone structure, including its two towers, but the spire and roof collapsed.
Full assessment of the damage is still being evaluated but early reports suggest it could have been much worse.
According to fire brigade spokesman Lt-Col Gabriel Plus, “the whole of the roof has been devastated… a part of the vault has collapsed, the spire is no more”.
However, junior interior minister Laurent Nuñez said that, had fire crews not entered the building, “without doubt it would have collapsed”, French newspaper Le Monde reported.
Miraculously, the building’s stained-glass windows of the 12th and 13th centuries seem to have been spared by the flames and the organ may have been damaged by water but not burned.
André Finot, spokesman of the cathedral, who was able to enter the nave during the night, said: “From what I could see, the stained glass had not been touched, the three beautiful roses that date back to the 12th and 13th century were still there.”
Some stained glass windows have suffered some damage, but these are newer.
He added: “They are stained glass windows from the 19th century, much less important, but not the jewels from the 13th century, it’s a bit of a miracle, we are very relieved.
“The organ would not have burned at all, but it could have suffered some damage because of the strong pressure of the water.”
There is still concern, however, for some of the paintings and artefacts within the building.
The Archbishop of Paris, talking to French TV station BFM, said: “Some paintings are impossible to remove.
“The damage is unthinkable because the paintings that could be removed, have been removed, but the paintings that are fixed to the walls in a certain way, you can not remove them just like that.
“It is a complicated situation, so I do not know in what state they are.”
There has already been an outpouring of generosity from the public to raise the funds for the reconstruction of the beloved landmark.
Two French billionaires, François-Henri Pinault and Bernard Arnault will donate €300m (£259m) between them to reconstruct the cathedral following the blaze.