The iconic cathedral caught fire on Monday evening and flames soon spread across the building.

The structure of the Notre Dame Cathedral has now been saved but the fabled building, widely considered a masterpiece of French Gothic architecture, has sustained serious damage.

Most notably, the spire and parts of the roof have collapsed after being engulfed in flames. Some stained glass windows have also been broken.

The historic Notre Dame Cathedral dates back to 1163

The precise cause of the fire is not yet clear but authorities said it may be linked to renovation work that was being done at the site.

Investigators are treating the fire as the result of an accident.

No fatalities have been reported in the blaze. One firefighter has sustained serious injuries.

Earlier, firefighters scrambled to save the building’s rectangular towers and its collection of valuable artworks and antiquities. A priceless crown of thorns and a tunic worn by Saint Louis in the 13th century were moved to safety but some paintings may have been damaged.

Paris’ Deputy Mayor Christophe Girard said the fire is a “tragedy for the world”. Thousands of Parisians watched as hundreds of firefighters worked to save the famous building.

French President Emmanuel Macron sped to the scene and said his thoughts were with “all Catholics and all French people.”

“Like all of my countrymen, I am sad tonight to see this part of us burn.”

“We’re thinking of the people of France”

Meanwhile, social media lit up with expressions of sorrow.

“Notre Dame is one of the world’s great treasures,” wrote Barack Obama. “And we’re thinking of the people of France in your time of grief. It’s in our nature to mourn when we see history lost – but it’s also in our nature to rebuild for tomorrow, as strong as we can.”

Obama’s successor as US President, Donald Trump, wrote: “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!” Later, he tweeted “God bless the people of France!”

Trump’s suggestion of water tankers was emphatically rejected by French authorities. The Interior Ministry’s Civil Security and Crisis Management agency tweeted employing such aircraft to fight the fire “could lead to the collapse of the entire structure of the cathedral”.

Theresa May also offered her condolences via Twitter: “My thoughts are with the people of France tonight and with the emergency services who are fighting the terrible blaze at Notre-Dame cathedral.”

“Heartbreaking scenes”

London Mayor Sadiq Khan was one of many to express solidarity with Paris. “Heartbreaking scenes” he wrote. “London stands in sorrow with Paris today, and in friendship always.”

Historian Camille Pascal told French broadcaster BFMTV that “invaluable heritage” was being lost in the fire. He appeared to be almost in tears.

“For 800 years the Cathedral has watched over Paris”, he said.

“Happy and unfortunate events for centuries have been marked by the bells of Notre Dame.

English actor Idris Elba simply wrote “I cannot believe what’s happening to Notre Dame”.

The cathedral is a UNESCO World Heritage site and one of the most historically important buildings in Europe. Henry VI of England and Napoleone Bonaparte were both crowned there.

Victor Hugo’s The Hunchback of Notre Dame, published in 1831, also helped cement the cathedral in the popular imagination. Depicting a building that was then bordering on decrepit, it inspired an extensive round of renovations.