"It is really going to be up to the French state and benefactors to help to restore and rebuild this", Robert Read, head of art and private client at Lloyd's of London insurer Hiscox told Reuters, adding it could take up to 20 years to restore the cathedral.
Firefighters are still examining damage and shoring up the structure after Mondays fire collapsed the cathedrals spire and destroyed the roof.
It was followed on Tuesday by a 200-million-euro pledge from Kering's rival luxury conglomerate LVMH and the family of its founder Bernard Arnault, France's richest person.
The promised assistance is a welcome - if late - surprise for the centuries-old Notre Dame, whose condition has been deteriorating for many years while the church and city government bickered over who should pay for much-needed repairs. A spokesperson said tour groups will probably still want to have a look at the cathedral, although French officials are not allowing any members of the public to get too close.
Experts are assessing the blackened shell of Paris' iconic Notre Dame cathedral to establish next steps to save what remains after a devastating fire destroyed much of the nearly 900-year-old building.
He also believes that Notre Dame will be restored, though that did not happen with St. Boniface Cathedral.
"Notre Dame was destroyed but the soul of France was not", Michel Aupetit, archbishop of Paris, said on RMC radio.
Officials consider the fire an accident, possibly as a result of the restoration work at the global architectural treasure.
Support came from outside France as well, with Apple chief Tim Cook announcing the tech giant would give an unspecified amount to help restore a "precious heritage for future generations".
Major European insurers expect France to bear the bulk of the cost of rebuilding the Notre-Dame Cathedral after a fire tore through the eight-centuries-old Paris landmark on Monday.
The heritage charity Fondation du Patrimoine said it was too early to estimate the cost of the damages.
"What we saw last night in Paris was our capacity to mobilize and to unite", Macron said, hailing France as a nation of "builders".
With the fire that broke out Monday evening and quickly consumed the cathedral now under control, attention is turning to ensuring the structural integrity of the remaining building.
The cost of a likely multi-year restoration project could itself take a year to become clear, industry experts said.
"I can say for the moment that local firefighters are linked with the church, whether it's a big church or a small church", he said. A 100m crane lowered the copper statues representing the 12 apostles and four evangelists onto a lorry.