Watching Notre Dame cathedral virtually destroyed in a massive blaze is heartbreaking, say stunned Rotorua people.

Firefighters managed to save the main structure and the building's two bell towers, despite two-thirds of the roof and Notre-Dame's iconic spire being destroyed.

The world-famous cathedral, which was built in 1160, was engulfed in flames after the fire broke out about 4.50am (NZT) today threatening precious artworks and one of the greatest architectural treasures of the Western world.

Tourists and Parisians looked on aghast from the streets below.

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French-born Rotorua resident Enora Moalic, 29, who has lived in New Zealand for almost four years, said she was horrified when her partner broke the news to her this morning.

"I'm from Brittany but I have visited Notre Dame a few times and really loved it. I was so looking forward to taking my partner Paul there one day," Moalic said.

"I thought the news reports may have exaggerated how bad the fire was at first, and it was something small they could quickly get under control.

"But when I saw the images of the roof and the spire collapsing I just couldn't believe my eyes. I thought 'oh my God no'. It's so, so sad. It's surreal, I'm still in shock," Moalic said.

"I really hope they can rebuild the cathedral. It is such a famous cathedral around the world and one of the places that everyone wants to see when they visit Paris.

"Paris just won't be the same without Notre Dame," she said.

French-born Esther Jacquet, who works at Casi Clinic in Rotorua, wept as she described how sad she felt watching images of the cathedral burning.

Jacquet said she and her three children had visited Notre Dame countless times over the years and the family last visited the cathedral in January.

"I was watching TV this morning and when I saw the images of the spire falling down my heart just sunk.

Four hundred firefighters desperately fought to save Notre Dame cathedral and its priceless treasures. Photo /AP
Four hundred firefighters desperately fought to save Notre Dame cathedral and its priceless treasures. Photo /AP

"Oh my God, it is really terrible. This is a landmark which is famous all around the world.

"Everybody wants to see Notre Dame when they go to Paris and I know it's been on many other people's bucket list. It's such a huge iconic part of Paris' history.

Notre Dame has survived so much over the years, including war and I still can't believe that it is almost lost to us," she said.

"Paris will never be the same without Notre Dome. I'm almost numb from the shock, it's heartbreaking," said a tearful Jacquet.

Parisian firefighters put their lives on the line by forming a human chain inside the burning cathedral to save many of its most important relics, including the Jesus Christ's Crown of Thorns.

Much-loved Notre Dame cathedral will be rebuilt says the French president Emmanuel Macron. Photo /AP
Much-loved Notre Dame cathedral will be rebuilt says the French president Emmanuel Macron. Photo /AP

French President Emmanuel Macron said the cathedral was part of France's destiny – and would be rebuilt starting tomorrow.

"We will rebuild because it is what French people expect, it is what our history deserves."

French police have launched an investigation into the cause of the fire, which potentially may be linked to the $10m (NZ) renovations being undertaken at the cathedral.

Twelve million people visit Notre Dame each year.