Investigators were working Tuesday to identify the source of a massive blaze that devastated the Notre-Dame cathedral in Paris, as church officials inspected the damage from a disaster that has sent shockwaves through France and the world.

Donations and offers of help began to pour in on Tuesday as day broke over the City of Light, revealing the extent of the damage from Monday night's inferno which took around 15 hours to extinguish.

"All night long I saw men going past with tears in their eyes. I described it this way: It was total chaos, but we can't let it knock us down," said Philippe Marsset, the vicar general of Notre-Dame.

French President Emmanuel Macron had also struck a defiant tone on Monday night as he visited the scene with his wife Brigitte, telling reporters: "We will rebuild Notre-Dame because it is what the French expect."

Around 400 firefighters battled through the night to control the flames, declaring only at around 10 am on Tuesday that it had finally been extinguished.

"Now we're in the phase of investigating," fire service spokesman Gabriel Plus told reporters.

A public appeal for funds was launched by the privately run French Heritage Foundation to help restore a "symbol of French history and culture".

Billionaires and local governments pledged nearly 500 million euros (565 million dollars) on Tuesday to help restore Notre-Dame cathedral, with foundations and crowd-sourcing sites also launching fund-raising drives.

French luxury group Kering, whose brands include Yves Saint Laurent and Gucci, kicked off the campaign late Monday with a promise of 100 million euros ($113 million).

That was followed Tuesday by a 200-million-euro pledge from its crosstown rival LVMH and the family of its founder Bernard Arnault.

The chief executive of French oil giant Total said the firm would contribute 100 million euros.

Other high-profile French donors so far included the investor Marc Ladreit de Lacharriere with 10 million euros, and construction magnates Martin and Olivier Bouygues, also with 10 million euros.

Pledges were also pouring in from anonymous donors to groups including the privately run French Heritage Foundation, which said it had already secured pledges totalling 1.6 million euros.

On a more modest scale, a fund set up by an "anonymous Parisian" on the Leetchi fundraising platform had topped 20,000 euros at midday Tuesday.

And the Hungarian city of Szeged promised to donate 10,000 euros to the reconstruction effort, in recognition of the help it received from the French capital after a devastating flood in 1879.

Paris Mayor Anne Hidalgo said Tuesday that the city would unlock 50 million euros, and proposed holding an international donors' conference in the coming weeks to coordinate the pledges to restore the gothic architectural masterpiece.

Specialised craftsmen and rare materials are also expected to be needed to restore the monument, which welcomes around 13 million visitors each year -- an average of more than 35,000 people a day.

The head of a French lumber company told AFP he would try to gather the 1,300 oak beams he figures are necessary to rebuild the intricate lattice that supported the now-destroyed roof, known as the "Forest".

But Sylvain Charlois of the Charlois group said finding big enough logs would not be easy, since "there aren't any stocks of cut wood in France available for a project this big."

The United Nations' Paris-based cultural agency UNESCO has promised to stand "at France's side" to restore the site, which it declared a world heritage site in 1991.

The German and Italian governments have also offered to help in the reconstruction, while Russian President Vladimir Putin offered to send "the best Russian specialists with rich experience in the restoration of national heritage monuments."

The inferno destroyed two-thirds of the roof of the 850-year-old UNESCO world heritage landmark, whose spectacular Gothic spire collapsed as orange flames and clouds of grey smoke billowed into the evening sky.

Late on Monday night, to the relief of the nation, Paris fire brigade chief Jean-Claude Gallet had declared that "we can consider that the main structure of Notre-Dame has been saved and preserved," as well as the two bell towers.

The Holy Crown of Thorns and a sacred tunic worn by 13th-century French king Louis, two irreplaceable artifacts, had been rescued along with the church's main crucifix, and placed with others at the Paris town hall.

The cathedral has figured as a central character through the ups and downs of French history since construction began in mid-12th century.

During the French Revolution in the 18th century, it was vandalised and plundered, but would go on to feature as a central character in a Victor Hugo novel published in 1831, "The Hunchback of Notre-Dame" which is credited with helping save it.

It survived the devastation of two global conflicts in the 20th century and famously rang its bells on August 24, 1944, the day of the Liberation of Paris from German occupation at the end of the World War II.

Asked how long the restoration could take, Eric Fischer, head of the foundation in charge of restoring the 1,000-year-old Strasbourg cathedral, which recently underwent a three-year facelift, said: "I'd say decades."

"The damage will be significant. But we are lucky in France to still have a network of excellent heritage restoration companies, whether small-time artisans or bigger groups," he told AFP

Fischer said the ability to rebuild the colossal cathedral in a manner that respects its original form and character would depend on the plans, diagrams and other materials available to the architects.

They would need "a maximum of historical data or more recent data gathered with modern technology such as 3D scans" of the kind used in the restoration of the Strasbourg cathedral, he said.

Stephane Bern, a TV presenter famous for his programmes on mediaeval France who was recently appointed the government's representative on heritage, estimated the rebuilding would take "10 to 20 years minimum".

Noting the restoration of Reims cathedral which was bombarded by German forces during World War I took decades, an emotional Bern, 55, told French radio: "You know what hurts me the most? It's the idea that I will not see it again in my lifetime."

"It will be rebuilt for future generations," he said.

German Chancellor Angela Merkel called Notre-Dame cathedral a "symbol of European culture" as the blaze raged.

The Vatican expressed its "incredulity" and "sadness" over the fire.