They stressed the unique and iconic place the monument has in human history and expressed solidarity with France.
"I hope the Notre-Dame cathedral may once again become, thanks to reconstruction work and the mobilization of all, a jewel in the heart of the city."
- Pope Francis
Notre-Dame "belongs to the whole of humanity. It has inspired writers, painters, philosophers and visitors who have come from all round the world."
- EU Commission head Jean Claude Juncker
UN Secretary General Antonio Guterres said he was "horrified" by the fire. UNESCO head Audrey Azoulay said the cathedral "represents an architectural, cultural and religious heritage, a unique literary heritage that speaks to the whole world."
"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!"
- US President Donald Trump
Chinese President Xi Jinping said his country was "deeply saddened" by the fire, state media reported. He called the building an "outstanding treasure of human civilization."
Prime Minister Narendra Modi "conveyed his shock and sadness" over the fire and "expressed India's solidarity with President and people of France on this national loss."
- Indian Foreign Minister spokesman
"Notre Dame is a historic symbol of France, a priceless treasure of European and world culture, one of the most important Christian sites. The tragedy that occurred overnight in Paris leaves sadness in Russians' hearts."
- President Vladimir Putin
"Notre-Dame is not only a symbol of Christianity in France, it is also our shared European heritage."
- German Chancellor Angela Merkel
"Prince Philip and I have been deeply saddened to see the images of the fire which has engulfed Notre-Dame Cathedral. My thoughts and prayers are with those who worship at the cathedral and all of France at this difficult time."
- Britain's Queen Elizabeth II
"I offer prayers to God so that he will help overcome the consequences of the fire and restore the cathedral to its former glory in the near future."
- Russian Orthodox Patriarch Kirill
"Tonight we pray for the firefighters tackling the tragic Notre Dame fire – and for everyone in France and beyond who watches and weeps for this beautiful, sacred place where millions have met with Jesus Christ."
- Archbishop of Canterbury Justin Welby
Iran's foreign minister, Javad Zarif, said his thoughts were with "the French and all Catholics," calling the cathedral "that iconic monument dedicated to the worship of our one God and that brought all of us closer through (Victor) Hugo's literary masterpiece."
"Notre Dame has for centuries stood proud and tall as an inimitable icon, a symbol of the country's great culture and history. We pray that... the destruction can be restored to allow this unparalleled structure to return to its position of symbolic majesty on the Parisian skyline."
- World Jewish Congress President Ronald S. Lauder
"Iraqis uniquely appreciate the pain, sense of loss afflicting the people of France as we have recently experienced destruction of much of our national cultural heritage."
- Iraqi President Barham Saleh
"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."
- US ex-president Barack Obama