In what was last night described as a national tragedy, flames consumed around a third of the interior of building, with some reports suggesting the famous Mackintosh library had been lost.
Widespread emotion and dismay was demonstrated on the streets of Glasgow, and echoed around the world as the news spread.
Hundreds of students, lecturers and shoppers gathered in Renfrew Street and Sauchiehall Street as flames were seen bursting out of windows on the upper floors shortly after noon.
Many wept at the sight of fire engulfing the A-listed school, completed in 1909 and recognisable across the globe as an Art Nouveau gem.
Last night there were no reports of injuries or loss of life.
Eyewitnesses said the fire appeared to have started after a projector exploded in the basement, where the school’s
archives are kept.
The blaze then consumed each of the five floors along the western half of the structure.
The Royal Institute of British Architects, which recently voted it the finest British building of the past 175 years, said the damage was an “international tragedy”.
“It is irreplaceable,” the institute said in a statement.
Scotland’s Deputy First Minister Nicola Sturgeon said it was “a national treasure”.
Broadcaster and writer Muriel Gray, chair of the board of governors at the art school, holding back tears, told The Scotsman: “I arrived as soon as I got the news.
“There’s no casualties and that’s the No 1 important thing.
“It’s so important to the world, one of the most important buildings in my life. I’m not moving until we know what’s happened.
“Everyone helping each other – it’s the people, that’s what makes it so special.”
She later described it as “a very black day”.
Fire chiefs last night said crews had “prevented the destruction of both the structure and the majority of its contents … more than 90 per cent of the structure is viable and protected up to 70 per cent of the contents – including many students’ work.”
Assistant chief officer Dave Boyle, of the Scottish Fire and Rescue Service, said: “Crews have been working absolutely flat out throughout this very challenging incident and it is clear their effort and skill has saved this treasured building and many of the items it housed.
“While the priority from the outset was to save life we have also been working closely with Glasgow School of Art staff to ensure firefighters conducted an effective salvage operation.”
Emergency crews arrived four minutes after the first call at 12:25pm, leading some individuals to safety while nearby buildings were evacuated.
Both the famous library and the Hen Run corridor on the top-level parts of the structure – known to staff and students as The Mack – appeared to be completely destroyed.
Jim Birrell, head of painting and printing, had been based in the art school for 20 years. He said: “It’s a tragedy. We’re in total shock. It’s Mackintosh’s masterpiece and it’s at least partially destroyed.”
Fourth-year fine art students had been hanging their work on Thursday night and yesterday morning before a 5pm deadline for their degree show.
Agat Weiss and Saule Zuk, both 26 and who lost their work, said there was no way to describe the loss of the building, but praised the spirit of the school.
Ms Zuk said: “People are really coming together – they are just great.”
“It’s very sad,” added Ms Weiss.
Final year painting and printmaking student Elizabeth Pirrie said: “There’s been a lot of tears over the last few hours but I suppose the main thing is that everyone is alive – it’s a complete miracle. It’s a stunning building. I didn’t realise just how important it was until today.”
By 6:30pm, Scotland’s chief fire officer Alasdair Hay said the main blaze was out but there were still pockets of fire within the building.
He said some objects of importance have been salvaged by firefighters, and structural engineers are assessing the safety and stability of the building.
The Mackintosh holds 300 items designed by the Glaswegian architect, as well as drawings, textiles, plaster casts, photographs and furniture in the archives.
The centre also included the recently acquired Stoddard Templeton archive, with thousands of designs, drawings and patterns from the luxury carpet-making companies ranging from Afghanistan to those of the Titanic.
Architecture lecturer at the GSA Mark Baines said: “It’s an architectural catastrophe. It is the loss of one of the most influential buildings and is the most inspired building ever constructed certainly in Glasgow.”
Iain Connelly, president of the Royal Incorporation of Architects in Scotland, said the profession was united in expressing its sorrow to students and staff.
He said: “The value of this building goes well beyond Glasgow or even Scotland.
“It is a work of architectural heritage of world renown and its influence upon 20th-century architecture is immeasurable.
“Scotland has seen the loss of an international treasure which reflects the genius of one of our greatest ever architects.”
Scottish culture secretary Fiona Hyslop said: “While thankfully nobody has been hurt in this fire, the destruction of this iconic building is devastating news and my thoughts are with staff and students who have seen the terrible loss of their workplace and academic work.”
She added: “This afternoon I have spoken to Professor Tom Inns, the GSA director, to relay our support and sadness at these awful events.”
Britain’s arts community, many of whom studied at the school, expressed their shock and sadness across social media yesterday. Three of the four candidates for this year’s Turner Prize have studied at the school, as well as a host of celebrities.