Macron vows to rebuild the Notre Dame Cathedral within five years

French President Emmanuel Macron says Notre Dame cathedral will be rebuilt "even more beautifully, " and that he wants the work done within five years

A massive fire on Monday ravaged the 850-year-old Gothic building, destroying much of its roof and causing its steeple to collapse.

The cathedral was minutes away from destruction, officials say.

But despite Macron's pledge experts say its reconstruction could take decades.

Fifty people will investigate the cause of the fire. Paris public prosecutor Rémy Heitz said there was no visible indication of arson and that the blaze was being treated as an accident.

A combined €800 million has already been pledged by several companies and business tycoons to help rebuild the Unesco World Heritage site.

READ MORE: More than €300 million pledged globally for reconstruction of the Notre Dame

In a televised address on Tuesday evening, President Macron suggested he wanted it rebuilt by the time Paris hosts the Summer Olympics in 2024.

"We'll rebuild Notre-Dame even more beautifully and I want it to be completed in five years, we can do it," said Macron, who had already pledged to launch an international fundraising scheme for the reconstruction.

"It's up to us to convert this disaster into an opportunity to come together... It's up to us to find the thread of our national project."

But Eric Fischer, head of the foundation in charge of restoring the 1,000-year-old Strasbourg cathedral, told AFP the Notre-Dame might take "decades" to rebuild.

Frédéric Létoffé, the head of the group of companies for the Restoration of Historic Monuments, put the timescale at between 10 and 15 years, warning substantial work would be needed to secure the site before restoration can begin.

The fire, which was discovered at 6:43pm on Monday and was fully extinguished almost 15 hours later, destroyed most of the cathedral's roof and led to the collapse of its iconic spire.

Experts have not yet been allowed on site to assess the damage and firefighters have sent a drone to survey the scale of the destruction.

Photos appear to show that at least one of the famed rose windows has survived, but there are concerns for some of the other stained-glass windows. The 18th Century organ has not been burned, but it is not clear whether it is damaged.

It was still too early to estimate the cost of the damage, said the Foundation du Patrimoine, an independent non-profit heritage group.

Deputy Interior Minister Laurent Nuñez said the structure was in excellent condition "overall" but that "some vulnerabilities" had been identified in the stone vaults and the remainder of the ceiling.

The main structure, including the two bell towers, was saved in a time window of 15 to 30 minutes by a team of 400 firefighters, he said.

In his speech Macron heaped praise on the fire services, saying they took "extreme risks" to tackle the blaze.