The roof of Notre Dame cathedral in Paris has collapsed after the building caught fire on Monday afternoon.
Footage posted online shows flames engulfing the upper part of the building, including the spire and bell towers.
Unconfirmed reports suggest most of the major religious and artistic relics, including the Crown of Thorns, were removed as the fire began.
The cause remains unclear, but officials have said say it could be linked to renovation work.
A major operation is now underway, officials added, and an area of Paris around the cathedral has been cleared.
Built between the 12th and 14th centuries, the cathedral is one of the most recognisable landmarks in the French capital, receiving more than 12 million visitors a year.
Cardinal Daniel DiNardo, President of the US bishops’ conference, called the fire “horrific.”
“This particular cathedral is not only a majestic Church, it is also a world treasure. Noble in architecture and art, it has long been a symbol of the transcendent human spirit as well as our longing for God,” the cardinal said.
“Our hearts go out to the archbishop and the people of Paris, and we pray for all the people of France, entrusting all to the prayers and intercession of the Mother of God, especially the firefighters battling the fire.”
Cardinal Vincent Nichols, President of the Bishops’ Conference of England and Wales, said: “It is an iconic building visited by millions but more importantly is a symbol of faith which is at the heart of Europe. We pray the fire is extinguished quickly & with a shared effort the building made good.”
Notre-Dame de Paris en proie aux flammes. Émotion de toute une nation. Pensée pour tous les catholiques et pour tous les Français. Comme tous nos compatriotes, je suis triste ce soir de voir brûler cette part de nous.
— Emmanuel Macron (@EmmanuelMacron) April 15, 2019
— Patrick Galey (@patrickgaley) April 15, 2019
BREAKING NEWS: Paris: Another Video shows spire at the iconic Notre Dame Cathedral partly collapsing following major fire: pic.twitter.com/jvdJgOMoUd
— BNL NEWS (@BreakingNLive) April 15, 2019
— Liam Taylor (@LiamMTaylor) April 15, 2019
— Firas El Echi (@FirasElEchi10) April 15, 2019
It’s getting worse. But the fire brigade has turned up. Hard to see how the tackle this. The plume of smoke is already 100s of feet long. pic.twitter.com/5LBf2odKka
— Shiv Malik (@shivmalik) April 15, 2019
Ave Maria pic.twitter.com/lb6Y5XV05a
— Ignacio Gil (@Inaki_Gil) April 15, 2019