Kier Construction Scotland, the main contractor in charge of restoring the Mackintosh Building at the Glasgow School of Art, has issued a short statement in response to the devastating fire which broke out on Friday.

The blaze, which happened at 11.20pm on Friday, is the second in four years to hit the Mackintosh Building, which was undergoing a multi-million-pound restoration project to return it to its former glory following the first fire.

Fire crews have spent a third day working to extinguish the blaze, which also damaged the O2 ABC venue.

The famous Mackintosh Library was to be restored to its original 1910 design using information from items retrieved and information gathered in an archaeological survey, along with consultation of Mackintosh’s original designs, early photography, letters and other documents.

The project to restore the building was helping to preserve traditional skills in the Scottish construction industry, as well as creating training and apprenticeship opportunities.

A Kier spokesperson said: “Kier has been working with the Glasgow School of Art since 2016 on the restoration of the Mackintosh building and so we share the devastation felt by the School and the wider public at this time. We are working closely with the Scottish Fire and Rescue Service in their investigation and as such it would be inappropriate to comment further whilst an investigation is ongoing.”

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.

However assistant chief officer David McGown said it will take some time to establish the full facts and circumstances.

ACO McGown, who is the SFRS director of prevention and protection, 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.

“It is of vital importance that we ensure the full facts and circumstances of this incident are clearly established.”

ACO McGown 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.”

A construction expert has suggested the Mackintosh Building may have to be demolished brick-by-brick and estimated the rebuilding cost to be at least £100 million.

Professor Billy Hare, a fire risk and construction management academic 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.”

The Glasgow School of Art (GSA) said while its immediate focus is on its students, they remain hopeful of a positive outcome for the building.

Muriel Gray, chair of the Board of Governors, GSA, said “First we would like to express our deep gratitude to the magnificent Scottish Fire and Rescue Service, and also to extend our sympathy to our neighbours, both residents and businesses, who have also suffered, very much including the beloved O2 ABC Glasgow.

“It is an understatement to say everyone is utterly devastated but as usual the GSA Executive Team, staff and students, have been outstanding, positive and supportive. We now have a difficult waiting game until Scottish Fire and Rescue Service, Glasgow City Council and associated agencies have completed their investigations into the condition of the building.

“We remain hopeful of as positive an outcome as possible because it is clear that the love for the Mackintosh and recognition of its importance to Glasgow and the wider world is shared by absolutely everyone.”

Professor Tom Inns, director – GSA, added: “We are strengthened by the continued messages and visible acts of support from our local community, our partners in Glasgow City Council, Scottish Funding Council, Historic Environment Scotland, the Scottish and UK Governments; and friends from across the world.”

Responding to the fire, First Minister Nicola Sturgeon said: “This is a very sad morning in the city of Glasgow. Glasgow School of Art is an institution that is loved not just by its students, staff and the people of this city, but by many around the world.

“The Scottish Government stands ready to provide any support that may be required, now and in the period ahead. I have been receiving regular updates and will continue to do so throughout the day. The Scottish Government’s resilience room was activated overnight and will provide any support necessary.”