Onlookers broke down in tears as the realisation began to sink in that the 169-year-old building - and its contents - could be destroyed.
When the fire happened, fourth-year students had been working on their degree show artworks, which were to be submitted by 5pm yesterday.
Other students and workers at the facility reported smelling burning, before there were scenes of panic as people rushed to safety.
In Renfrew Street, as firefighters tried to battle flames, horrified students, staff and members of the public looked on in disbelief. Some architecture students, who were in the basement, where the fire is believed to have started, were taken to another building.
It is not known how many people were inside when the fire took hold but it is likely to have been busy.
Saule Zuk, 26, said she couldn't believe what had happened.
She said her artwork for her degree show, which was to start next month, is destroyed.
She said: "We were on the first floor and I saw the smoke and flames coming out the ventilation. My installation is going to be burned. The heat was just immense."
Another student, who asked not to be named, believed a projector pointed at a foam art installation, had overheated and caught fire.
She said: "Students are doing all kinds of things for their final artworks. People are working with expandable foam which is highly flammable."
Austin Yuill, who works at the art school, said: "As far as I know it started from a spark which has gone on to foam, expanding foam."
ANGEL Reid, 20, a third-year student who lives in Shawlands, said: "There was a lot of crying, a lot of running, a lot of panic.
"People didn't know what was happening. You hear a fire alarm but you never think it's a fire.
"But we saw the flames and the smoke and we had to get out.
"It is devastating. I don't know what's going to happen about all the students' work that's destroyed.
"And people come to this art school because of this building. It's part of Glasgow."
Former student Jack Farrell, 23, who is a tour guide for the art school, said: "The building is so old, with all the turpentine and wood any fire would spread quickly."
Jon Young, 34, a former student who lives in the West End, was helping his friend with an art installation at the time.
He said: "We heard a bang then saw smoke coming out of walls and got out.
"All their work is ruined. I don't know how they'll repair everything."
A staff member, who asked not to be identified, said she panicked while trying to get out of her office on the top floor.
She said: "Our fire exit is at the bottom of the building but I kept seeing flames and smoke so came out the main entrance.
"There was talk of the students using a lot of equipment for their installations - soldering, foam, projection boxes - so it seems like something has gone wrong.
IT'S not just their artwork, it's the building and the archives and the library and everything else that's been there for years."
Ambrose Gillick, an architecture lecturer at the art school, said he was shocked at how quickly the fire took hold.
He said: "I was at my computer at the time and just smelled burning.
"I thought it was my computer but then I noticed it was coming from the basement.
"It is a terrible tragedy of a national significance.
"It is the most beautiful building in Scotland, if not the UK.
"The school is close-knit and we identify ourselves very closely to the building.
"People come to the art school to study in that building."