Mr McGown said the service was determined to establish not only the cause of the fire, but how it spread, and what safety measures were in place at the building, which is considered the masterpiece of architect and designer, Charles Rennie Mackintosh.
Four appliances remained at the scene yesterday afternoon tackling a few remaining pockets of fire at the scene. The inferno broke out in the historic Mackintosh Building at 11:19pm on Friday, before spreading to nearby buildings, including the O2 ABC venue.
The blaze is the second in four years to hit the building, which was undergoing a multi-million-pound restoration project to return it to its former glory after a 2014 fire.
Mr McGown said: “The investigation into this devastating incident has already commenced.
“Our fire investigation team has started gathering information and, working alongside our police partners, will look at various sources of information to establish exactly what has happened here. However, I would like to stress that this is a very complex process and will take time.”
He added: “Our fire investigations team are specialists in their own field.
“They will look at every aspect of this incident – including the cause of the fire, how it spread and what safety measures were in place.
“We understand the need for clarity here and why so many want to know how this happened, but I would again like to reiterate that we need to establish the full facts and circumstances of this incident – and this will take time.”
At the height of the incident more than 120 firefighters were involved in fighting the blaze. There have been no reports of any casualties.
The blaze has shocked and saddened people in Glasgow and beyond including leading figures in entertainment.
Singer Annie Lennox tweeted: “So sad and disappointed for everyone affected by this 2nd devastating fire... (who would believe??!!) at Glasgow’s historic and renowned Charles Rennie Mackintosh art school. .. the renovators, students, staff, alumni, noble fire-fighters and everyone in Glasgow.”
Experts have estimated the cost of rebuilding the gutted Mackintosh Building would be at least £100m in the event that anything can be salvaged at all.
However, Glasgow School of Art officials said they remain hopeful of a positive outcome for the Mackintosh Building,
Last night Culture Secretary Fiona Hyslop said a multi-agency group of conservation experts had been set up which would play a “vital role” in the weeks and months ahead.
Meanwhile, a charity which works to improve access to music and dance for disabled people said it has lost thousands of pounds due to the fire.
Paragon Music was due to hold its annual Jamathon fundraiser event in the nearby Centre for Contemporary arts, but access remains closed off.