A large fire has broken out at the Glasgow School of Art for the second time in four years.
Flames and plumes of smoke engulfed the world-renowned Mackintosh building in the city centre.
Nearby buildings have been evacuated as fire crews tackle the blaze, which spread "in the space of a few minutes" when it started just after 23:00 BST.
The building was ravaged by fire in May 2014 and a multi-million pound restoration project was under way.
'Like a tinder-box'
A Scottish Fire and Rescue Service spokeswoman said "a number of engines" were sent to the scene, where crews were "working hard to extinguish the well-developed fire".
Ben, an eyewitness, told the BBC the fire looked "much worse" than the one which had taken hold in 2014.
"This is a blaze, the building is just going up like a tinder-box. It's quite shocking."
At the Scene
Lesley Roy, BBC News
The blaze has completely engulfed the Mackintosh building once again. The building was still a construction site from the fire four years ago.
Loud bangs can be heard coming from inside as crews try to tackle the flames.
Students - some of whom graduated today - are in the street in shock. They can't believe it's happened again.
Police Scotland advised the public to avoid the area, and said areas around Dalhousie St, Scott St and Sauchiehall St were all affected by road closures.
Glasgow North East MP Paul Sweeney described the building, designed by Charles Rennie Mackintosh, as "the most architecturally important building in Glasgow".
The Labour politician said the restoration effort had suffered a "horrific setback" which he hoped would be overcome.
"We cannot lose this building," he added.
In a tweet, Scottish First Minister Nicola Sturgeon said: "This is clearly an extremely serious situation.
"My first thoughts tonight are for the safety of people - but my heart also breaks for Glasgow's beloved @GSofA.
"Once again, we are indebted to the bravery of our firefighters and other emergency services."
The Mackintosh building was completed in 1909 based on designs by Charles Rennie Mackintosh, Scotland's most-lauded designer.
It has been described as "a working art school as well as a work of art", and has an A-list rating from Historic Scotland.
The fire in 2014 destroyed the building's library, which was recognised as being one of the finest examples of art nouveau in the world.