PARIS (CBS/AP) — A catastrophic fire engulfed the upper reaches of Paris’ soaring Notre Dame Cathedral as it was undergoing renovations Monday, threatening one of the greatest architectural treasures of the Western world as tourists and Parisians looked on aghast from the streets below. The cathedral’s roof collapsed in the massive blaze, along with the spire. Paris prosecutors say they think the fire was started accidentally and some of the structure has been saved.

Officials also believe firefighters are making progress in stopping the flames from spreading.

CBS3’s Vittoria Woodill is on vacation in Paris with her husband and went to the cathedral during their first day in the city.

“It’s extremely disappointing and disheartening and makes us all sick to our stomach,” said Woodill.

Woodill reported live on CBS Philly’s Facebook page during the fire.

“It’s absolutely terrible,” Woodill said during a Facebook Live. Video showed flames collapsing the cathedral’s roof.

“You can feel the emotion and shock in the air. Everyone is out their windows, out their doors, watching this happening,” explained Woodill.

Woodill said people have been gathering in the streets and singing songs of prayer.

The cathedral is home to incalculable works of art and is one of the world’s most famous tourist attractions.

“Everything is burning, nothing will remain from the frame,” Notre Dame spokesman Andre Finot told French media.

As Paris firefighters battled the blaze, part of the spire of the 12-century monument collapsed.

WATCH: Notre Dame Cathedral in Paris engulfed in flames during the holiest week of the year for Catholics https://t.co/Q2Pt0kHC83 pic.twitter.com/NF3noBEzvz — CBS News (@CBSNews) April 15, 2019

Paris police said there were no deaths so far and the origin of the fire was unknown. French media quoted the Paris fire brigade saving the fire is “potentially linked” to a $6.8 million renovation project on the church’s spire and its 250 tons of lead.

Flames shot out of the roof behind the nave of the cathedral, among the most visited landmarks in the world. Sights of the flames stopped passers-by in their tracks along the Seine River that passes beneath the cathedral.

French President Emmanuel Macron postponed a televised speech to the nation because of the stunning blaze and was going to the cathedral himself.

Deputy mayor Emmanuel Gregoire said emergency services were trying to salvage the famed art pieces stored in the cathedral.

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, the cathedral’s architecture is famous for, among other things, its many gargoyles and its iconic flying buttresses.

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.

The cathedral was immortalized in Victor Hugo’s “The Hunchback of Notre Dame,” published in 1831, and has long been a subject of fascination in popular culture as well as the traditional art world.

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.”

Associated Press reporters at the scene saw massive plumes of yellow brown smoke filling the air above the Cathedral and ash falling on the island that houses Notre Dame and marks the center of Paris. As the spire fell, the sky lit up orange.

Paris Mayor Anne Hidalgo is in despair at the “terrible fire.” Hidalgo said in a Twitter message that Paris firefighters are 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.

So horrible to watch the massive fire at Notre Dame Cathedral in Paris. Perhaps flying water tankers could be used to put it out. Must act quickly! — Donald J. Trump (@realDonaldTrump) April 15, 2019

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.”

Philadelphia Archbishop Charles Chaput said in a statement the “ongoing destruction being wrought by flames is doubly sorrowful as it comes during the holiest week of the Christian calendar.”

“I ask the clergy, religious, and lay faithful of the Archdiocese of Philadelphia to join me in prayer to the Blessed Mother for the protection of fire personnel and first responders in Paris working to battle the blaze and provide for the safety of the community. We also pray that our Lord will bring comfort and peace to Archbishop Michael Aupetit as well as our brothers and sisters in the Diocèse de Paris, and the people of France at this time. In the face of desolation and devastation, we find hope in the Resurrection,” said Chaput in a statement.

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)