LEADING architects described the destruction of the iconic building as an "international tragedy".

Politicians, community leaders and Glasgow celebrities also spoke of their shock at the scale of the devastation.

The Royal Institute of British Architects (RIBA) said: "Damage to a building of such immense significance and uniqueness is an international tragedy. It is irreplaceable."

RIBA President Stephen Hodder said: "The RIBA joins our colleagues in Scotland in sending out a message to the students, staff of the school and all those who have been associated with this building over the decades, a message of sorrow and commiseration at this terrible, terrible news.

"The institute will do anything it can to help in any way."

Antiques Roadshow expert Steven Moore wrote: "Seeing Glasgow School of Art on fire is heartbreaking. Its like watching a dear friend in agony and you're unable to help. I feel sick."

Fran Healy, who studied at GSoA before becoming lead singer with the band Travis, expressed his sadness on Twitter.

He said: "Just super super sad this place which has been with Glasgow and with all the students is burning down..."

Architecture critic Hugh Pearman said: "This can't happen. We can't lose Mackintosh's Glasgow School of Art. It's unthinkable."

Elsewhere, art and architecture websites were inundated with messages of support and sympathy from around the world for Glasgow and the GSoA's students and staff.

Scotland's Deputy First Minister Nicola Sturgeon said: "The Mackintosh Building is not just part of Glasgow's heritage - it is a national treasure."

Community leaders also spoke of their shock.

SNP MSP and Evening Times columnist Humza Yousef said: "I just hope such an iconic national treasure can be salvaged."

The UK Government said it will contribute to the costs of restoring the art school.

Speaking in Glasgow today, Chief Secretary to the Treasury Danny Alexander said: "We've seen the appalling damage to the Glasgow School of Art.

"It's a hugely important building not just for Glasgow and Scotland but for the whole of the United Kingdom.

"I can tell you that the UK Government will be willing to make a significant financial contribution towards the cost of rebuilding.

"Obviously at the moment we don't know the precise extent of the damage or what the costs will be, so I can't put a figure on it, but the Chancellor and I have spoken this morning and we both think it is appropriate."

He added: "This is going to be a costly business but it's a very important landmark for the whole of the UK so we stand ready to provide an appropriate share of the funds that will be necessary to bring this hugely important building back to life."

Mr Alexander said the Government would contribute "in the millions, if necessary" to restore what he described as a "priceless gem".