PARIS – Notre Dame Cathedral was perhaps only minutes away from total destruction when Monday's blaze swept through the medieval building, authorities said.

At least 30 firetrucks, vehicles and even boats on Paris’ River Seine responded quickly to the blaze – most reaching the scene within 11 minutes, according to French firefighters.

One of the first firefighters on the scene said the fast response was related to the deep knowledge of the inside of the 850-year-old house of worship. “We knew the church really well because we had done a lot of drills there,” Chief Cpl. Miryam Chudzinski said Wednesday at a news conference.

Chudzinski recounted that when she arrived at the scene and saw large crowds watching, and in many cases filming the fire with their phones, she realized the scale of what they were dealing with. “We are proud of how we handled it,” she said.

Gabriel Plus, a representative for the Paris Fire Brigade, said Wednesday that at least 60 members of his organization remain at Notre Dame to check the cathedral’s structural integrity.

“When the fire reached the center of the cathedral, a robot was brought in, and my firefighters were pulled out, to douse the flames,” Plus said. “It was too dangerous for them once the flames reached the spire.”

Donations neared the $1 billion mark and recovery efforts ramped up Wednesday at the charred cathedral.

Priceless relics and historical treasures were saved from a devastating fire that left Paris – and much of the world – in shock.

Engineers and historians are likely to put up a temporary roof to protect the cathedral from the elements, assess damage and salvage materials before beginning repairs that may take decades.

Plus said the building’s outer buttresses are secure, but some damaged stonework will be cleared. Scaffolding damaged in the fire – part of renovation work before the blaze – will be removed.

Structural engineers, stained-glass experts and stonemasons from across the globe are likely to head to Paris to help with restorations in the next few weeks.

Photos from inside the building give a glimpse of the herculean task ahead: They show piles of burned and blackened debris on the cathedral floor.

Outside the landmark Wednesday, there were fewer onlookers than in recent days, but crowds of residents and tourists were still snapping selfies and taking pictures of what they could glimpse of the church's exterior from outside a security zone.

"It's like something you see in the movies," said Liam Mcilduff, 15, a student from a nearby school who marveled at all the activity.

The cost to completely repair the church will reach $1.13 billion to $2.3 billion, according to Stephane Bern, who heads heritage renovation programs across France.

Bern said about $995 million was raised in just a day and a half from French business leaders and ordinary worshipers at home and abroad. The French government is gathering donations and setting up a special office to deal with them.

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French President Emmanuel Macron pledged to "make the cathedral of Notre Dame even more beautiful," calling for the building to be rebuilt in five years. France, he said, would "convert this disaster into an opportunity." Macron is holding a special Cabinet meeting Wednesday dedicated to the Notre Dame.

"It's such an exceptional monument. It's precious, made by our ancestors," said Aime Cougoureux, the owner of Ma Bourgogne, a popular restaurant near the Victor Hugo museum. Hugo, one of France's most celebrated writers, played a large role in popularizing Notre Dame. His 1831 novel "The Hunchback of Notre Dame" is about the cathedral's deformed bell-ringer Quasimodo who falls in love with Esmeralda. The book saw a serious spike in sales on Amazon in France this week.

"Paris needs Notre Dame," Cougoureux said. "The tourists love it, too, especially Americans. When there are no Americans in Paris, it's an economic crisis."

Emily Bessie, 43, a tourist from Maine, took photos Wednesday from a vantage point that gives a view of where 400,000 firefighters doused water on the cathedral's destroyed spire. She said her friends in the USA shared images on social media of their own visits to the cathedral.

"Even though the circumstances are clearly very different, we in the U.S. know what it feels like to lose a symbol of your country," she said, referring to the collapse of the twin towers of New York City's World Trade Center during the 9/11 terrorist attacks in 2001.

Paris’ public prosecutor Remy Heitz said Tuesday the cause of the fire that tore through the cathedral, causing its wooden roof and spire to collapse, was not known, although investigators are "favoring the theory of an accident" possibly linked to extensive renovation work. There were no signs of arson, Heitz said.

About 30 people have been questioned in the investigation, which Heitz warned would be “long and complex.” Among those questioned are workers at the five construction companies involved in renovating the church spire and roof when the fire broke out.

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The cathedral's 18th-century organ suffered some burn damage but has not been lost, Olivier Latry, one of the church's three organists, told USA TODAY.

French Deputy Interior Minister Laurent Nunez said efforts to save the cathedral’s stone structure and two towers "came down to 10 to 15 minutes."

Nunez said fires were stopped before they had an opportunity to spread and it was only this "small window" and the heroic efforts of firefighters who formed a human chain to save relics that staved off more damage.

American art historian Andrew Tallon used laser technology to completely digitally map Notre Dame in 2015, creating a replica that could help architects and engineers rebuild the Gothic cathedral.

Pope Francis, the leader of the world's 1.2 billion Catholics, used his weekly audience Wednesday at St. Peter’s Square in Rome to express his sadness over the fire at Notre Dame, the seat of the Paris archdiocese. "I feel very close to all of you," he said.

Some weren't thrilled by the idea of contributing money toward the cathedral's reconstruction. "I already pay my taxes. Why should I give any more?" said a bookseller who runs a stall on a quay alongside the Seine opposite Notre Dame. He would be identified only by his first name, Matthias.

Contributing: Kristin Lam