PARISIANS have been told to expect a “long and complex” investigation into the cause of the fire at Notre Dame, though officials say there is, as yet, no evidence of foul play.

“We are favouring the theory of an accident,” Paris Prosecutor Remy Heitz said.

The fire in the cathedral was fully out by yesterday morning and, miraculously, the building remains structurally sound.

However, the damage to the cathedral’s wooden roof, and the iconic 300 ft spire is catastrophic and will cost hundreds of millions of euros to repair.

“We will rebuild Notre Dame,” French President Emmanuel Macron insisted on Monday night, “because that is what the French expect.”

The cathedral was, he added, “our history, our literature, the epicentre of our life ... The cathedral of every French person, even those who have never visited it.”

Macron said a national appeal would be launched as soon as possible.

Yesterday, there were separate pledges of €100 million from the billionaire Pinault family, French energy company Total, and L’Oreal and the Bettencourt-Schueller Foundation. The family of Bernard Arnault, owners of the luxury goods group LVMH Moet Hennessy Louis Vuitton, said they would contribute €200m.

The mayor of Paris, Anne Hidalgo, said the city would provide €50m and organise an international donors’ conference.

French culture minister Franck Riester said some of the most valuable treasures in the cathedral had been stored overnight in the Paris town hall and would be moved to the Louvre museum “as soon as possible”.

He said major paintings were not likely to be removed until Friday morning, adding: “They have not been damaged but there could be some damage from the smoke so we are going to take them safely and place them in the Louvre where they will be dehumidified and they will be protected, conserved and then restored.”

One of the relics saved on Monday night is a piece of the crown of thorns worn by Jesus Christ at his crucifixion.

Heitz revealed that the alarm was first sounded at 6.20pm and despite checks no fire was found.

It was only when a second alarm went off 23 minutes later that fire was discovered in the “forest” the wooden framework of beams in the attic.

Just under 400 firefighters worked for more than 12 hours through the night, battling to stop the complete destruction of the 850-year-old Gothic building.

Two police officers and one firefighter were injured during the blaze.

In a message to Macron, the Queen praised the emergency services “who have risked their lives to try to save this important national monument”.

Bishop Hugh Gilbert, the president of the Bishops’ Conference of Scotland offered his solidarity with the archdiocese in Paris: “Beyond the tragedy, Easter remains. Fire cannot thwart the essential purpose of Notre Dame or any church building.

“Wherever it may be, God’s people – the living stones – will still come together to celebrate the resurrection of Christ and hope reassert itself.”

Meanwhile, European Council president Donald Tusk called on the EU’s member countries to help, saying the site in Paris is a symbol of what binds Europe together.

“The burning of the Notre Dame cathedral has again made us aware that we are bound by something more important and more profound than Treaties. Today we understand better the essence of that, which is common, we know how much we can lose. And that we want to defend it – together.”

The fire also focused minds in Westminster, with fears the crumbling Houses of Parliament could be susceptible to a similar catastrophic blaze.

Labour leader, Jeremy Corbyn, said the French inferno should be a wake-up call for authorities here: “You see beautiful buildings like that and think of the beautiful buildings we’ve got in this country. If any of those were destroyed in fire how would we feel about it? The state of the building is very poor in Westminster and a fire risk is obviously huge with a building that has so much wood within it.”

There were 40 fires in Parliament between 2008 and 2012, though all were quickly put out by wardens.

A multibillion-pound programme of restoration is due to start in the mid-2020s, with MPs moving out while work is carried out.

House of Commons leader, Andrea Leadsom, said the fire was a “crucial reminder of the importance of preserving our historic buildings”.