The Glasgow School of Art has been devastated by a huge fire, only four years after parts of the building were destroyed by a smaller blaze.

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More than 120 firefighters and 20 appliances were called to tackle the blaze, which began at about 11.15pm on Friday and spread to a neighbouring music venue, the O2 ABC.

The grade-A listed building appears to have been gutted by the fire and had its roof and upper floors destroyed. Firefighters were unable to enter the building because of fears its walls might collapse.

Residents said the heat was so intense it could be felt several streets away, with chunks of blazing timber and debris raining down on neighbouring streets. Police evacuated 27 people from nearby properties as a precaution, but there were no reported casualties.

Facebook Twitter Pinterest An aerial view of the damage caused to the Mackintosh Building in Glasgow. Photograph: Police Scotland Air/PA

On a visit to the scene on Saturday, Scotland’s first minister, Nicola Sturgeon, said the “heartbreaking” fire had been “much, much worse than the one that took hold of the Mackintosh building four years ago – so the damage is severe and extensive”.

“There are assessments and discussions ongoing with the fire service and building control about the structure of it and it’s structural safety. Obviously all of us hope the building can be saved but I think it’s too early to draw any conclusions from that, she said.

Iain Bushell, a deputy chief officer with the Scottish fire and rescue service (SFRS), said: “The roof is gone completely. We cannot get in yet to assess the damage. I can only see from the street but it looks as if the building has been extensively damaged.”

Facebook Twitter Pinterest Photograph: Rocco Giudice @81Rocco

Alan Dunlop, an architect and academic based in Glasgow who trained at the school, said: “The building does look as though from the inside it’s been totally gutted. All that seems to remain is the stone walls.”

The damage to the building’s stonework raises questions about whether the structure will survive this second round of intense heat.

In the last fire, the stonework endured temperatures of up to 1,000C and was then cooled down very quickly by water, leaving some of the stone cracked and and too weak to reuse.

The building was designed by the art nouveau architect and designer Charles Rennie Mackintosh, whose designs extended to the smallest detail, including its furniture, lamps and glass inlays.

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Its most famous feature was its library, which housed many rare and archival materials as well as original furniture and fittings, and was gutted by the first fire.

The city celebrated the 150th anniversary of Mackintosh’s birth last week, when one of his other famous buildings, the Willow Tea Rooms nearby, reopened after a refurbishment.

Students at the school had their graduation ceremony on Friday, said Jane Sutherland, the chair of the local community council and an artist who graduated from the school in 1982.

Glasgow School Art (@GSofA) Huge congratulations to all of our graduates today! Group photographs for all schools are available on our Flickr site now: https://t.co/sn6jV19VO4 pic.twitter.com/ol2cEkpjff

She said she witnessed the fire from her flat and saw the start of the blaze in 2014. “This time around I feel numb, like ice, legs like jelly,” Sutherland said. “The fire was immense. People were dodging fist-sized flaming embers last night. All the neighbours were out; we were all worried all the roofs were going up. This area is full of architectural gems.

“It was terrifying last night. The smell of it and you could feel the heat of it two blocks away.”

She said the firefighters had been heroic. “They fought with their lives for that building; they did the last time and they have again.”

Margaret Archbold, who studied sculpture at the art school in the early nineties, said that she was relieved to see some stone left from her vantage point at the police cordon in Hill Street.

“It should have been the safest building in Glasgow,” she said. “It’s so ironic that all that money was put back in to restoring the building and celebrating the Mackintosh anniversary. It’s devastating to see when you know what’s in that building.”

Another witness, Aidan Dick, said the fire and smoke grew in intensity “in the space of a few minutes”. He tweeted: “Glasgow School of Art is on fire again. Heartbreaking. My thoughts go to all students and staff, and I hope no one was caught in the blaze.”

Bushell said: “The fire was well alight in minutes and after that it went very quickly, so the school of art is extensively damaged. It did spread to the ABC theatre on the other side of the street, so the roof is extensively damaged from that.”

The 2014 fire began when flammable gases from a foam canister used in a student project were ignited accidentally. A report by the SFRS concluded that old ventilation ducts helped it spread into neighbouring studios and upwards through the building.

The report also noted that a sprinkler system, designed to enhance existing fire protection measures, was in the latter stages of installation at the time of the fire, but was not yet operational. It is not known whether any similar system had been installed yet in the latest restoration.

Facebook Twitter Pinterest The Glasgow School of Art. Photograph: Murdo Macleod/The Guardian

Restoration work had been in constant progress since the summer of 2014, beginning with debris removal, then the salvage process conducted by specialist forensic architects, and the drying out of the building to guard against future difficulties with rot.

The restoration had been scheduled to conclude by the end of 2018, with undergraduate students returning to the building in 2019.