Fire chiefs are confident they will discover the cause of the blaze which engulfed Glasgow School of Art.
Eight appliances remained at the scene on Monday following the fire, which broke out in the historic Mackintosh Building and spread to nearby buildings including the O2 ABC.
The blaze, which happened at 11.20pm on Friday, is the second in four years to hit the Mackintosh Building, which was undergoing a multimillion-pound restoration project to return it to its former glory.
The Scottish Fire and Rescue Service (SFRS) said the investigation into the cause of the blaze has already started and they believe they will be able to pinpoint how it started.
SFRS assistant chief officer David McGown said: “Our fire investigation process swings into action as soon as our operational crews begin on the scene.
“Our fire investigation will look into quite a vast array of information.
“They have a complex task ahead of them and of course they’ll look at situations and issues such as which fire safety measures were in place beforehand, what was supposed to be in place, witness statements, CCTV footage and, working with our partners, collate that information into what will be the one truly informed source of what actually happened in this fire.”
He added: “I think it’s very important for people to understand that it is a complex process to investigate such a scale of fire and it will take time.
“The reason it takes time is not because we want it to take a specific length of time but the reason is that we want to conduct an absolute comprehensive and professional investigation into what happened and I can give this guarantee that we will find out what happened in this fire, what the cause was and what the cause of spread was.”
A police cordon will remain in place around the area for the “foreseeable future”, with parts of Sauchiehall Street, Hill Street, Dalhousie Street, Renfrew Street and Garnethill Street all closed.
A few small pockets of fire remain within the building and crews remain at the scene to dampen down any hotspots.
Experts have estimated the cost of rebuilding the gutted Mackintosh Building would be at least £100m.
Professor Billy Hare, a fire risk and construction management academics at Glasgow Caledonian University, said: “It remains to be seen if it will be possible to retain a facade from the current building.
“If not, damaged buildings have been taken down almost stone by stone in the past and rebuilt with a new, internal frame.
“This sort of project will cost a great deal more than the estimated #35 million after the last fire in May 2014.”
However, GSA bosses said they remain hopeful of a positive outcome for the Mackintosh Building.
Meanwhile, Labour MP for Glasgow North East Paul Sweeney, who is director of the Glasgow Building Preservation Trust, said that, having been escorted round the building by SFRS, it is clear the interior is almost entirely lost but that the main structural beams appear to still be largely intact, giving hope that some of it can be saved.
Tweeting about his visit he wrote: “The Mack will endure.”
He told the BBC: “Whatever needs to happen to make this building realised again as Mackintosh’s vision has to happen.
“This is building is the pinnacle of achievement of British Art Nouveau architecture and it’s my job as a Member of Parliament to go down and say this building ought to be saved for the nation.”