French President Emmanuel Macron vowed to rebuild Notre Dame Cathedral within five years after a devastating fire Monday caused the landmark's roof and spire to collapse.
"We now have to get things done," Macron said in an address Tuesday. "We will act and we will succeed."
Monday's devastating fire was likely sparked accidentally, prosecutors said Tuesday.
Outside the building, the cathedral's two bell towers and outer walls stood firm, while their insides and the upper structure were eviscerated by the blaze.
Investigators will not be allowed inside the cathedral until experts can verify that the structure withstood the heat and it is safe for them to enter.
As investigators look into what started the fire, a drive to rebuild the cathedral has already received more than $700 million in pledges, according to Reuters.
More than 400 firefighters battled the blaze for 15 hours. The fire was largely extinguished, saving the 8½-century-old building from "total destruction," according to a French fire official. The two iconic rectangular bell towers were saved even though the fire spread to one of them Monday evening.
No deaths were reported, but two police officers and a firefighter were injured. The blaze erupted around 6:50 p.m. Paris time Monday, luckily after it had closed to the public. The destruction came during Holy Week, six days before Easter.
Pope Francis said Tuesday that he shared the sadness of the French people mourning the devastation.
"I associate myself with your sadness, as well as that of the faithful of your diocese, the inhabitants of Paris and all the French," Francis said in a message to the archbishop of Paris, Michel Aupetit.
French Culture Minister Franck Riester said Tuesday some of the most valuable pieces of art inside Notre Dame were saved and relocated, including the crown of thorns and the tunic of St. Louis, which have been relocated to Paris City Hall. Other artworks will be transferred to the Louvre Museum, he said.
"The worst has been avoided, but the battle isn't fully won yet," Macron said Monday outside of the cathedral. He also expressed his sympathies to Catholics around the world, the people of Paris and the people of France.
Among the donations pledged to rebuild were from two of France's richest people. Francois-Henri Pinault, whose Artemis holding company owns a controlling stake in luxury group Kering, pledged 100 million euros ($113 million), while Bernard Arnault, chair of LVMH, gave 200 million euros.
In addition, French energy company Total pledged 100 million euros and French luxury and cosmetics group, L'Oreal along with its owners, the Bettencourt Meyers family, and the Bettencourt Schueller foundation, said they would donate 200 million euros.
The city of Paris has pledged 50 million euros to the restoration.
Residents living close to the cathedral were evacuated in case the building collapsed, said Paris Mayor Anne Hildago. The area surrounding the cathedral, Paris' Ile de la Cite, was also evacuated, according to Reuters.
The Paris prosecutor's office opened an investigation into the fire soon after the damage began. Late Monday, prosecutors said their preliminary findings suggested the huge fire had been started accidentally. The building had been undergoing renovations.
"We are favoring the theory of an accident," Paris public prosecutor Remy Heitz told reporters on Tuesday. About 50 people are now working on a probe into what caused the fire, he said.
Le Bras Freres, the company working on the cathedral's restorations, said it will be cooperating fully with the investigation.
"All I can tell you is that at the moment the fire began none of my employees were on the site. We respected all procedures," said a representative of Le Bras Freres, a family firm.
Investigators have started questioning witnesses and 15 construction workers who were at the site on Monday, NBC News reported.
Firefighters at the scene directed much of their efforts toward saving the artwork stored at the back of the cathedral, which had been undergoing renovations.
Notably, 16 religious statues were removed from the cathedral for cleaning on Thursday — for the first time in over a century — and therefore escaped the fire.
The cathedral, which dates to the year 1163 and is famous for featuring in Victor Hugo's classic novel "The Hunchback of Notre-Dame," attracts millions of tourists every year.
President Donald Trump offered his condolences to Macron on Tuesday, according to White House press secretary Sarah Huckabee Sanders.
"The United States stands with French citizens, the city of Paris, and the millions of visitors from around the world who have sought solace in that iconic structure. The Cathedral has served as a spiritual home for almost a millennium, and we are saddened to witness the damage to this architectural masterpiece," the statement said.
"Notre Dame will continue to serve as a symbol of France, including its freedom of religion and democracy. France is the oldest ally of the United States, and we remember with grateful hearts the tolling of Notre Dame's bells on September 12, 2001, in solemn recognition of the tragic September 11th attacks on American soil. Those bells will sound again. We stand with France today and offer our assistance in the rehabilitation of this irreplaceable symbol of Western civilization. Vive la France!" the statement said.
Trump on Monday encouraged France to use "flying water tankers" to put out the fire. French firefighters didn't use an aircraft to dump water on the cathedral, a strategy that France's civil defense agency dismissed on Twitter.
"Helicopter or airplane, the weight of the water and the intensity of the drop at low altitude could indeed weaken the structure of Notre-Dame and result in collateral damage to the buildings in the vicinity," the agency wrote.
Later, Trump tweeted his prayers.
Parisians mourned the destruction of the city's symbolic center. The cathedral has not undergone such damage in its more than 800 year history.
"I'm devastated," Elizabeth Caille, 58, who lives nearby, told NBC News. "It's a symbol of Paris. It's a symbol of Christianity. It's a whole world that is collapsing."
— Reuters, The Associated Press and NBC News contributed to this report.