Part of the support structure around Notre-Dame Cathedral's rose windows is to be dismantled to prevent further damage following a massive fire.
The Culture Ministry's fire expert, Jose Vaz de Matos, told reporters on Wednesday part of the triangular structure above the central rose window is to be taken down "to limit the movement" of the stone.
De Matos said the main risk to the cathedral is the gables above the rose windows, which provide crucial support to the stained glass masterpieces.
He said the structure is particularly exposed to the wind, and the overall structure remains fragile.
Police officials told The Associated Press that the triangular structure is leaning 20 centimetres forward towards the street since the fire.
Monday's fire destroyed most of the lead roof of the 850-year-old architectural treasure and caused its spire, which was added in the 19th century, to collapse.
Despite extensive damage, many of the cathedral's treasures were saved, including Notre Dame's famous rose windows, although they are not out of danger.
Paris Firefighters' spokesman Lt-Col Gabriel Plus said that even though they are in good condition, a "threat" continues to the gables, or support walls, because of the heavy stone statues perched on top of them.
"The roof no longer holds (the gables) up. They are holding up all by themselves," he said, adding that some statues must be removed to lessen the weight on the gables.
Scaffolding that had been erected for a renovation of the spire and roof must also be properly removed because of its weight and because it is now "crucially deformed", he added.
The cathedral is still being monitored closely by firefighters and experts to determine how much damage the structure suffered and what needs to be dismantled to avoid collapse.
Nearly 900 million euros ($A1.4 billion) has been pledged for the cathedral's restoration, and French President Emmanuel Macron has vowed to finish it in five years, in time for the 2024 Olympics in Paris.
Experts, however, have questioned that ambitious timeline for such a massive operation. Even Prime Minister Edouard Philippe acknowledged on Wednesday that it would be difficult.
Prominent French conservation architect Pierluigi Pericolo told Inrocks magazine it could take triple that time.
"No less than 15 years ... it's a colossal task," said Pericolo, who worked on the restoration of the 19th-century St-Donatien Basilica, which was badly damaged in a 2015 blaze in the French city of Nantes.
He said it could take between two to five years just to check the stability of the cathedral that dominates the Paris skyline.
"It's a fundamental step, and very complex, because it's difficult to send workers into a monument whose vaulted ceilings are swollen with water," Pericolo told France-Info.
"The end of the fire doesn't mean the edifice is totally saved. The stone can deteriorate when it is exposed to high temperatures and change its mineral composition and fracture inside."
Notre Dame's rector said he would close the cathedral for up to "five to six years", acknowledging that "a segment" of the structure may be gravely weakened.
Pledges for the restoration have come from ordinary worshippers and wealthy magnates, including those who own L'Oreal, Chanel and Dior. Presidential cultural heritage envoy Stephane Bern told broadcaster France-Info that 880 million euros has been raised since the fire.
Criticism already has surfaced in France from those who say the money could be better spent elsewhere, on smaller, struggling churches or on workers.
Macron called a special cabinet meeting on the fire, which investigators believe was an accident possibly linked to the renovation that was already under way.