But many have taken heart from developments on Tuesday: news, for example, that the cathedral’s three irreplaceable “rose” stained glass windows survived without “catastrophic” damage.

In his speech, Macron said the fire had been a traumatic experience for the French and for the world.

He praised firefighters who had taken “the most extreme risks” to save the building.

And he reminded France that in their history “towns, cities, ports and churches have been burned down or destroyed by wars and revolutions, and every time we rebuilt”.

“I share your pain and I also share your hope. We now have to get to work.”

French government ministers met on Tuesday to begin drawing up a reconstruction plan for Notre-Dame.

There were continuing concerns about the cathedral’s structure, and firefighters and engineers were closely monitoring the building’s stability.

Junior interior minister Laurent Nunez said “some weaknesses” had been found and engineers were urgently working to prop up the walls.

"Globally the structure is holding up well, but some weaknesses have been identified particularly in the vault and the gable of the northern transept, which have to be secured," he told reporters at the scene, adding that five neighbouring buildings had been evacuated.

A fire expert told the BBC the restoration work was very likely the cause of the fire, as it involves the use of solvents and heating elements, and there is very little else in a roof that can spark such a blaze.

"Nothing suggests that it was a voluntary act," prosecutor Remy Heitz told reporters at the cathedral.

He said a fire alarm had been raised at 6.20pm on Monday evening but a search found no fire – nevertheless the building was evacuated. A second alert 23 minutes later revealed fire in the roof frame, spreading out of control.

A team of 50 investigators have already identified and interviewed around 30 renovation workers who were on site. However for safety reasons their access to the cathedral itself is still limited.

Minister of Culture Franck Riester told French radio station France Inter "the main structure has been saved but there is still a lot of instability, the situation is still precarious".

"Last night, two thirds of the roof burned, the spire collapsed, creating a hole in the vault, part of the transept collapsed."

The United Nations cultural agency UNESCO, based in Paris, has already started contacting experts and declared itself ready to “send an emergency mission to assess the damage, preserve what can be preserved and plan short and medium-term measures”, director-general Audrey Azoulay said.

France’s Minister of Culture Franck Riester said the three huge 13th century stained glass “roses” on the north, west and south transepts “have not suffered catastrophic damage”, though it is unclear how much damage they did sustain. The heat of the fire could have partly melted both the glass and the lead that binds it together.

A church steward told French radio the main organ, some of whose pipes date back to the 15th century, also escaped major damage from either the fire or the firefighters’ water, though it was covered with dust. Another smaller organ suffered some water damage, as firefighters drenched the interior to try to protect old wooden choir stalls.

Some of the hundreds of artworks in the building were believed lost in the fire, though many were saved.

Some artworks will be in the Louvre within 24 hours being restored or repaired, however other big works cannot be taken off the cathedral walls yet, due to safety concerns in the building.

Riester said there was no apparent fire damage to the big paintings, but some smoke damage.

“We will transport them safely to the Louvre where they will be dried, protected, preserved and restored,” he said.

Riester also confirmed the church's two most hallowed relics had been saved: a crown of thorns said to have been worn by Christ and a tunic worn by Saint Louis, a 13th-century French king.

The Paris prosecutor, whose investigation opened before the fire was out, confirmed his team of 50 investigators are still working on the assumption it was an accident, probably related to restoration work at the site.

Five companies were working on the site at the time.

Meanwhile, private sector donations to a rebuilding fund continued to grow.

Oil giant Total plended €100 million ($157m), joining 100 million from luxury goods mogul Bernard Arnault’s family, and 100 million from retail billionaire Francois-Henri Pinault’s family fund.

Tim Cook’s Apple also pledged a company donation to the rebuilding effort.