Investigators sifting through the fire-ravaged Notre Dame Cathedral in Paris warned of potential weaknesses in the remains of the building Tuesday, as experts said it could take months just to identify the scale of the reconstruction task. While the building was assessed to be structurally sound overall, pictures showed gaping holes in the roof where the ancient vaulted ceiling had collapsed into the nave. French Junior Interior Minister Laurent Nunez said experts had identified “some vulnerabilities” in the building, particularly in the roof, much of which has been destroyed, and part of the north transept. Some nearby residential properties were evacuated as authorities assess the scale of the damage from the blaze that engulfed the medieval landmark Monday night. Firefighters said it took more than nine hours before the flames were brought under control. It was not immediately known what caused the fire, which began on Monday evening in the attic, according to the Paris Fire Brigade. The cathedral, and its central spire – an area where the fire was first visible to onlookers – had been surrounded by scaffolding amid construction work. Scores of priceless artifacts were rescued from the flames, and will be taken to the Louvre museum for safekeeping. Paris prosecutors have opened an investigation, but on Tuesday Prosecutor Rémy Heitz said “nothing shows that it’s an intentional act,” and that the start of the fire was “likely accidental.” Heitz also said that the investigation, which is in its early stages, is expected to be a long process. Lt. Col.Gabriel Plus, a spokesman for the fire brigade, said internal security officers first heard the fire alarm at 6:20 p.m. (12:20 p.m. ET) and began to evacuate the cathedral, even though they didn’t see any sign of fire. François-Xavier Lochet, a 70-year-old worshiper, said the alarm interrupted a Mass. Lochet said he noticed visitors began to get ushered out but those who had gathered for the service remained and the priest resumed. He said Mass continued until a police officer went up and told the priest, “This is no joke. You’ve got to get out.” Twenty-three minutes later, the fire alarm rang again, Plus said. That’s when the cathedral’s security officers noticed the flames. Firefighters were unable to save the cathedral’s 19th century spire, which burned to a blackened shell before toppling as thousands of Parisians who had gathered in the streets watched in horror. Two police officers and a firefighter suffered minor injuries, the brigade said. A day after flames engulfed the cathedral, hundreds of people marched on Paris’ streets Tuesday night, praying and singing hymns together. Pledge to rebuild French President Emmanuel Macron said he wants the cathedral to be rebuilt in five years. “We will rebuild Notre Dame even more beautiful and I want that to be done in the next five years,” Macron said in a televised address to the nation on Tuesday night. “Throughout our history, we have built towns, ports, churches. Many have been burnt due to revolutions, wars, due to mankind’s mistakes. Each time we have rebuilt them. “The fire of Notre Dame reminds us that our story never ends. And that we will always have challenges to overcome. What we believe to be indestructible can also be touched,” Macron added. At the scene of the fire on Monday night, Macron had vowed to reconstruct “because that is what the French expect, that is what our history merits, and this is our deep destiny.” But Frédéric Létoffé, the co-president of a group of French companies specializing in restoring historic buildings, cautioned that full restoration of the Gothic cathedral could take significantly longer – around “10 to 15 years.” He told reporters earlier Tuesday that the site will need to be secured before any restoration work can take place. “This will require a lot of work since, beyond shoring and reinforcement, it will be necessary to build a scaffolding with an umbrella to be able to cover the entire roof that went missing, to ensure protection against weathering” he added. Pledges of funding to help the restoration work were flooding in on Tuesday, with more than $700 million in donations from French business leaders and businesses confirmed by Tuesday afternoon. They include a €200 million ($226 million) donation by the family of French billionaire businessman Bernard Arnault and his LVMH luxury goods group, a €112.2 million (approximately $126.5) pledge from the French Heritage Foundation, and a €200 million ($226 million) donation from the Bettencourt Meyers family, L’Oréal group and the Bettencourt Schueller Foundation. Valérie Pecresse, president of the Île de France region, told CNN affiliate BFMTV that the region will provide €10 million ($11.13 million) of emergency aid for Notre Dame, and Paris Mayor Anne Hidalgo said she would host a fundraising conference at Paris City Hall in the coming weeks. French Interior Minister Christophe Castaner said it could take months to assess the damage. Shock and horror On Tuesday, the city was reeling from the aftermath of the blaze. Most French political parties suspended their European election campaigns. Nathalie Loiseau, a former Europe minister and a candidate for Emmanuel Macron’s “La République en Marche” party, said the party’s campaign would be suspended “until further notice.” “We are going through a profound moment of sadness,” Loiseau said in a tweet. Many people gathered near the site on Tuesday, paying their respects to a landmark that to Parisians, and to some 13 million visitors each year, is a symbol of the French capital. “For me, it’s much more than stones, it’s a part of myself that is burning,” Paris resident Sarah Virot, 32, said as she looked up at the charred church in front of her. As the fire raged on Monday night, thousands of Parisians and tourists stood, horrified, in front of the 850-year-old-Gothic masterpiece. Some sang hymns as, a few days before Easter, one of the symbols of French Catholicism burned in front of them. “It’s awful to see such a symbol disappearing in front of you. It’s been there for so many years and in a few minutes half of it disappeared,” local Thibaud Binetruy said. “Paris without Notre Dame, madness.” Another witness, Anne Marie, spoke with tears in her eyes. “In Paris, it’s a monumental symbol – every person with different religions are really moved and saddened,” she said. “Paris without the cathedral is not Paris anymore.” Messages of support and mourning have poured in from around the world. The Vatican said the Holy See learned with “shock and sadness the news of the terrible fire that has devastated the Cathedral of Notre Dame de Paris, symbol of Christianity, in France and in the world.” The fire “goes beyond Paris,” said the city’s archbishop, Michel Christian Alain Aupetit. “I received a supportive message from the chief rabbi of Paris. Everyone is writing in to share their feelings. This goes beyond Paris. People are reacting worldwide.” Turkish Foreign Minister Mevlut Cavusoglu described the fire as a “disaster for all humanity,” while London Mayor Sadiq Khan said the British capital “stands in sorrow” with Paris. “Heartbreaking scenes of Notre Dame cathedral in flames. London stands in sorrow with Paris today, and in friendship always,” Khan said on Twitter. US President Donald Trump also weighed in, calling it a “terrible, terrible fire.” His suggestions on how to tackle the conflagration were less welcome than his sympathy however. The French Civil Security Agency pushed back against Trump tweeting that “flying water tankers could be used to put it out,” pointing out that dropping water on the ancient church could cause its collapse. Works of art, artifacts saved Images of flames engulfing the cathedral – a UNESCO world heritage site since 1991 and one of Paris’s most popular tourist sites – were splashed around the globe. But as shocking as the scene appeared, it could have been so much worse. Its iconic facade and towers were salvaged, as were a host of invaluable artifacts and works of art stored inside, including the Holy Crown, believed by many to be from the crown of thorns placed on the head of Jesus during the crucifixion, and which the cathedral calls its “most precious and most venerated relic.” On Tuesday, Culture Minister Franck Riester said the most precious works of art including the “crown of thorns” and the “tunic of Saint Louis” had been moved from Notre Dame and are now being held under security at Paris City Hall. Speaking to reporters, Riester said the rest of the artworks would be moved to the Louvre museum. Among the parts of the church worst affected by the fire was also one of the newest: The spire, which was built in the 19th century. That will have to be rebuilt entirely, as will the far older roof structure, known as “the forest.” “The framework from the 13th century is called a forest, because it required a forest of trees to build it,” said Patrick Chauvet, the rector of the cathedral. The framework was completely lost in the fire, he added. A symbol of France Notre Dame’s foundation stone was laid in 1163 by Pope Alexander III, and the cathedral was completed in the 13th century. With its towers, spire, flying buttresses and stained glass, it is both an architectural jewel and a major religious and cultural symbol of France. Located on the Ile de la Cite, a small island in the center of Paris, the cathedral is one of the city’s most popular attractions, drawing an estimated 13 million visitors a year. Even as it fell into disrepair over the centuries, it was the site of Napoleon Bonaparte’s coronation as emperor in 1804. A broad restoration effort was launched in the mid 19th century, partly buoyed by the success of Victor Hugo’s novel “The Hunchback of Notre-Dame” in 1831. Fresh renovation works were underway before the fire. A small silver lining from the blaze may be that the restored spire and roof will be built to modern standards and better equipped to withstand future fires. Experts have pointed to other fires at historical sites, such as that which engulfed the UK’s Windsor Castle in 1992, which were followed by comprehensive restoration projects. Windsor took five years to restore, but is now in a better state than before the blaze.