World leaders on Tuesday expressed shock and sympathy over the devastating fire that razed Paris’ famous Notre-Dame cathedral overnight.

Notre-Dame is one of France's most-visited landmarks and a masterpiece of Gothic architecture with more than 850 years of history. Construction began on the cathedral in 1163 and it opened in 1345.

More than 500 firefighters fought throughout Monday night and into Tuesday against the flames that burned at least two-thirds of the cathedral’s roof and caused the collapse of its spire.

Its two bells towers were saved from the fire, which originated from unknown causes. Officials believe the fire began accidentally and may be linked to building work, but an investigation has been launched. One firefighter was seriously injured while fighting the blaze, reports say.

The French government said the structure of the cathedral looked to have been saved.

France’s President Emmanuel Macron said that "the worst has been avoided" in the fire, although he added that "the battle is not completely won" and announced that he wanted to rebuild it “all together.”

The Vatican received the news of the "terrible" fire with "shock and sadness,” while the interim spokesman of the Holy See, Alessandro Gisotti, expressed the "closeness" of the Vatican to French Catholics and Parisians and assured that everyone would be kept in their prayers.

The president of the European Commission, Jean-Claude Juncker, shared the emotion of the French nation, saying that "Notre-Dame of Paris belongs to the whole of mankind” and has inspired writers, painters, philosophers and visitors from all over the world.

The British Prime Minister, Theresa May, also showed her support for France: "My thoughts are with the people of France tonight and with the emergency services who are fighting the terrible blaze at Notre-Dame cathedral," she said.

German Chancellor Angela Merkel said in a message through her spokesman Steffen Seibert that she was “saddened to see these terrible images of Notre-Dame, symbol of France and of our European culture, in flames. Our thoughts go to our French friends.”

But the King of Spain, Philip VI, was confident that the Parisian cathedral "will rise from its ashes.”

"The French people will rebuild it, will undoubtedly set it upright again. And we will be there, the whole world is and will be with France. The Cathedral of Notre-Dame will rise from its ashes," the monarch tweeted.

Spain’s Prime Minster Pedro Sanchez also used social media networks to express his condolences.

"The fire at Notre-Dame is a catastrophe for France and for Europe. The flames have ravaged 850 years of history, architecture, painting and sculpture. This will be difficult to forget. France can count on us to recover the greatness of its heritage," he said.

On the other side of the Atlantic, the United States’ President Donald Trump even suggested the use of “flying” tankers to put out the flames.

"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!" he wrote on Twitter.

However, the French Civil Security agency swiftly rejected Trump's suggestion.

"Hundreds of firemen of the Paris Fire Brigade are doing everything they can to bring the terrible #NotreDame fire under control. All means are being used, except for water-bombing aircrafts which, if used, could lead to the collapse of the entire structure of the cathedral," it said on Twitter.