Bells will toll at cathedrals around France on Wednesday evening in honor of the monument. Remarkably, no one was killed in the fire, after firefighters and church officials speedily evacuated the site during a mass.
On Monday, the storied Paris landmark caught fire in what is being treated as an accident. The massive fire burned for hours, sending up plumes of smoke visible across the city.
THE CATHEDRAL'S FUTURE
Macron said Tuesday in a televised address to the nation that "we will rebuild Notre Dame cathedral even more beautiful."
He added that "we can do it and once again, we will mobilize" to do so.
Macron, who also said "we have so much to rebuild," thanked firefighters and police and donors who are giving money for the renovation.
Macron's 5-year deadline - which happens to coincide with the 2024 Paris Olympics, which the government wants to make a major showcase - struck many as unrealistic.
Pierluigi Pericolo, in charge of restoration and security at the St. Donatian basilica in Nantes, said it could take two to five years just to secure Notre Dame, given its size.
"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," he said on 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."
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Though an official told ABC News that it will likely be at least three years before members of the public are able to visit the Notre Dame Cathedral again, a bishop later said it would be up to six years.
Bishop Patrick Chauvet, the church's rector, said "a segment of the cathedral has been very weakened" by the devastating fire. He did not elaborate which section he was talking about.
He added it was unclear what the church's 67 employees would be doing in the future.
The Paris prosecutor said Tuesday morning there's no evidence of arson in the Notre Dame fire and that they're working on the assumption that the blaze was an accident.
Remy Heitz says the investigation will be "long and complex."
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Speaking Tuesday, after the blaze was put out, he said five investigators are working on the probe. He says they will be interviewing workers from five companies that had been hired to work on renovations to the cathedral's roof, which was being repaired before the fire and which is where the flames first broke out.
Later in the day, Paris judicial official said investigators have questioned about 30 people after the fire at Notre Dame Cathedral.
He said most of them were employees working on the renovation of the monument.
The official, speaking anonymously on an ongoing investigation, said the cathedral's fire alarms sounded twice on Monday evening.
The first time, some people, including a fire official permanently working on the site, went to check under the roof and saw nothing. The second time it was already too late because the fire was too strong, the official said.
He added that 40 to 50 investigators are working on the case but are not allowed to enter the monument yet for safety reasons.
ALMOST $1 BILLION DONATED TO REBUILDING EFFORTS
Nearly $1 billion has already poured in from ordinary worshippers and high-powered magnates around the world to restore the fire-ravaged Notre Dame Cathedral in Paris, after the French president set a controversial five-year deadline to get the work done.
The country's richest businessman, Bernard Arnault, and his luxury goods group LVMH pledged 200 million euros ($226 million).
A communique said that the Arnault family were "in solidarity with this national tragedy, and join in the reconstruction of this extraordinary cathedral, a symbol of France, of its heritage and togetherness."
Businessman Francois-Henri Pinault and his billionaire father Francois Pinault also said they were immediately giving 100 million euros (about $113 million) from their company, Artemis, to help finance repairs.
PHOTOS: A look inside Notre Dame Cathedral during the fire
Oil and gas giant Total said it would contribute 100 million euros "to help the reconstruction of this architectural jewel."
Cosmetics maker L'Oreal promised the same amount to rebuild "a symbol of French heritage and of our common history."
Among other contributors, Bouygues construction group CEO Martin Bouygues said he and his brother Olivier would donate 10 million euros.
Firefighters declared success Tuesday morning in their more than 12-hour battle to extinguish the flames that engulfed Paris' iconic Notre Dame cathedral.
What remained was a blackened shell of the monument that had survived almost 900 years of tumultuous French history.
The two iconic 69-meter bell towers remained intact and swarmed with building specialists and architects at dawn, looking tiny from the ground as they conducted analysis. The cathedral's spire and roof were gone, however.
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Paris firefighters spokesman Gabriel Plus said "the entire fire is out" and that emergency services are currently "surveying the movement of the structures and extinguishing smoldering residues."
"The task overnight was to bring the fire under control so it doesn't re-start," said Junior Interior Minister Laurent Nunez in front of the cathedral.
"The task is - now the risk of fire has been put aside - about the building, how the structure will resist," he continued.
MORE ON THE ICONIC LANDMARK
Built in the 12th and 13th centuries, Notre Dame is the most famous of the Gothic cathedrals of the Middle Ages as well as one of the most beloved structures in the world.
Situated on the Ile de la Cite, an island in the Seine river, its architecture is famous for, among other things, its many gargoyles and its iconic flying buttresses. Some 13 million people visit it every year.
It is the subject of countless stories and works of art, notably Victor Hugo's novel, The Hunchback of Notre Dame, which helped rally support for Notre Dame's massive renovation in the 19th century and which was later adapted into an animated Disney movie. After the fire, the original version of the novel shot to the top of the Amazon bestseller list in France and also climbed to the top of the historical fiction category in the U.S.
Among the most celebrated artworks inside are its three stained-glass rose windows, placed high up on the west, north and south faces of the cathedral. Its priceless treasures also include a Catholic relic, the crown of thorns, which is only occasionally displayed, including on Fridays during Lent.
"It's not one relic, not one piece of glass - it's the totality," said Barbara Drake Boehm, senior curator at the Metropolitan Museum of Art's medieval Cloisters branch in New York, her voice shaking as she tried to put into words what the cathedral meant. "It's the very soul of Paris, but it's not just for French people. For all humanity, it's one of the great monuments to the best of civilization."
French historian Camille Pascal told BFM broadcast channel the blaze marked "the destruction of invaluable heritage."
"It's been 800 years that the Cathedral watches over Paris," Pascal said. "Happy and unfortunate events for centuries have been marked by the bells of Notre Dame."
He added: "We can be only horrified by what we see."
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"It's heartbreaking," ABC News Senior National Correspondent Terry Moran reflected. "Notre Dame is not just a church, it's the heart of France. It is a place that is a testament to the history of France and a place that the French people have rallied around in times of trouble. It is also a place that is built to the glory of God. So this is a tragedy not just for the people of France, but also for the people of the Christian faith around the world."
ABC News contributor Alastair Bruce said it may take many years for the church to be rebuilt.
"I would imagine that this is the greatest tragedy to the arts of France that we are witnessing now, and it will take almost 100 years to put it right," he said.
REACTIONS FROM PARIS AND BEYOND
Macron posted on Twitter in French with a message that translates to, "Notre-Dame de Paris in flames. Emotion of a whole nation. Thought for all Catholics and for all French. Like all our compatriots, I am sad tonight to see this part of us burn."
Notre-Dame de Paris en proie aux flammes. Émotion de toute une nation. Pensée pour tous les catholiques et pour tous les Français. Comme tous nos compatriotes, je suis triste ce soir de voir brûler cette part de nous.— Emmanuel Macron (@EmmanuelMacron) April 15, 2019
Crowds stopped in their tracks along the Seine River, which passes under the island where the cathedral stands.
Eyewitness John Dickas told ABC News it is heartbreaking for bystanders who are watching the efforts to fight the blaze.
"For me, the most heartbreaking moment was when I saw - about 20 minutes after I started watching the fire - I saw the ladders go up and the hoses start spraying," he said. "It was just heartbreaking to watch. The ladders were not tall enough. The hoses were not strong enough. This was, just clearly, a fire beyond the capacity of the crews' capability. I mean, they were clearly doing everything they could. It was just so much bigger and so much more out of control than they had the resources to deal with."
Paris Mayor Anne Hidalgo said in a Twitter message that Paris firefighters were still trying to limit the fire and urged Paris citizens to respect the security perimeter that has been set around the cathedral.
Hidalgo said Paris authorities are in touch with the Paris diocese.
Reactions from around the world came swiftly including from the Vatican, which released a statement expressing shock and sadness for the "terrible fire that has devastated the Cathedral of Notre Dame, symbol of Christianity in France and in the world."
In Washington, Trump tweeted: "So horrible to watch the massive fire at Notre Dame Cathedral in Paris" and suggested first responders use "flying water tankers" to put it out.
Cardinal Timothy Dolan, the archbishop of New York, said he was praying "to ask the intercession of Notre Dame, our Lady, for the Cathedral at the heart of Paris, and of civilization, now in flames! God preserve this splendid house of prayer, and protect those battling the blaze."
ABC Owned Television Stations and ABC News contributed to this report.