In what was described as a “French moonshot” President Emmanuel Macron vowed to rebuild Notre-Dame Cathedral within five years but breakneck pace triggered doubts that the building could be restored in a short timeframe. In a wide-ranging televised speech on Tuesday evening, Mr Macron said the 19th century spire, vaulting and two-thirds of the cathedral's roof would be completed in time for the Paris 2024 Olympics. The central Paris landmark was gutted by a fire on Monday evening, sparking an outpouring of grief for the 12th-century building. Firefighters are still examining damage and shoring up the structure after the blaze collapsed the cathedral's spire and destroyed the roof. "We will rebuild the cathedral to be even more beautiful and I want it to be finished within five years," Macron said. However, the tight timeline seems unrealistic to experts. 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," Mr Pericolo said. Mr Pericolo worked on the restoration of the 19th century Saint-Donatien basilica, which was badly damaged by fire in 2015 in the French city of Nantes. He said it could take between "two to five years" just to check the stability of the massive cathedral that dominates the Paris skyline. However Jack Lang, a prominent former Culture minister, said the state must mobilise to complete the project within as little as three years. "I hear since yesterday that it will take a decade, it's a joke! We must give ourselves a short deadline, as we have done in the past for exceptional projects,” he said. The prime minister Edouard Philippe announced architects from around the world will be given the opportunity to compete to design the restoration of Notre-Dame cathedral in a move that could pave the way for the look of the building to change radically for the first time since the mid-19th century. The brief is for experts to decide if the 295-foot tall spire should be restored identically, or "give Notre-Dame a new spire that is adapted to the techniques and the challenges of our era," Mr Philippe told a press conference in Paris Wednesday. Donors have so far pledged more than 800 million euros for the effort with prominent business people and ordinary citizens alike parting with their cash. The cost of any renovation is not yet known, said Mr Philippe. The Walt Disney Company is the latest in a string of benefactors to declare support, pledging $5m to the cause. Later on Wednesday, Mr Philippe tweeted on the "historical responsibility" his government bears to ensure the restoration is done correctly. "The President of the Republic has expressed an ambition. That of rebuilding Notre-Dame de Paris in five years. This is obviously a huge challenge. A historical responsibility. The construction of our generation for the generations that will succeed us," he posted. In Tuesday’s speech, Mr Macron drew a parallel between political unrest in his country and the fate of the cathedral. "I profoundly believe that it is up to us to transform this catastrophe into an opportunity to come together and think about what we were and what we need to become, to improve ourselves,” he said. The Gilet Jaunes protests have dragged on for almost six months. Originally a simple protest over fuel tax rises, it blossomed to include grievances over wider societal issues. In February, the French parliament passed an anti-hooligan bill to curb violence in cities across the country. The bill bans protesters from hiding their faces, gives police greater powers to extract people from demonstrations, and grants local authorities the right to ban individual protesters. Sixty Paris firefighters remain at the scene. The service says the cathedral's rose windows are in good shape but that their support structures are at risk. Meanwhile, extremists have attempted to capitalise on the fire using social media to promote messages of hate and make threats of attacks. Platforms have failed to stop the spread of misinformation, despite promises in the wake of terror attacks to curb fake news and material that fuels the sense of crisis around major events. The SITE monitoring group picked up messages from the ISIS-linked Al-Muntasir group with a poster of the blazing cathedral accompanied by the words: “Have a good day”. The channel previously published videos that celebrated the 2015 terror attacks in France. The cathedral was targeted in 2016 by a vehicle laden with gas canisters but the attack was foiled and three people were arrested. French officials have so far ruled out a terrorist motive but have questioned around 30 people in connection with the blaze. Most were builders and others involved in existing renovation work. Sixty Paris firefighters remain at the scene. The service says the cathedral's rose windows are in good shape but that their support structures are at risk. Paris prosecutor Remy Heitz said the most likely cause was an accident and that 50 investigators had been assigned to the “complex” probe into what happened on Monday night. Mayor of Paris, Anne Hidalgo, announced an exhibition would be set up to tell the story of the cathedral over the course of the works. The cathedral’s rector, bishop Patrick Chauvet, said it will be closed to worshippers and visitors for five to six years.