Glasgow's world-renowned School of Art has been gutted by another huge blaze, four years after part of the building was destroyed by fire.
Flames ripped through the celebrated Mackintosh building after it caught fire at around 23:15 BST on Friday.
The blaze has spread to nearby buildings, including the Campus nightclub and O2 ABC music venue, which suffered "extensive damage".
No casualties have been reported, the Scottish Fire and Rescue Service said.
Efforts to bring the fires under control are expected to be "prolonged", Deputy Chief Officer Iain Bushell said.
More than 120 firefighters have been sent to the scene, faced with "an extremely challenging and complex incident", he added.
The Mackintosh building was badly damaged by fire in May 2014 and was due to re-open next year following a multi-million pound restoration project.
Ben, an eyewitness, told the BBC the latest fire looked "much worse" than the previous one.
"This is a blaze, the building is just going up like a tinder-box. It's quite shocking," he said.
Connor Neil, 22, said people were being evacuated from their homes and there was a "big orange light" which could be seen from streets away.
At the Scene Lesley Roy, BBC News
Despite the thick, black, acrid smoke, the blaze seemed to be dying down in the Mackintosh building.
But very quickly the situation changed, with the roof of Campus nightclub catching fully alight.
Earlier, loud bangs were heard coming from inside the art school as crews tried to tackle the flames.
Students - some of whom graduated on Friday - were 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.
Mr Sweeney went on to say: "The 1909 library extension, that was the origin of the 2014 blaze, is now fully alight too.
"It looks like the entire interior space is now fully alight.
"The best we can probably hope for is structural facade retention and a complete rebuild of the interior. Devastating."
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.
In recent years, the school has produced many of the UK's leading contemporary artists such as Douglas Gordon, David Shrigley, and three recent Turner Prize winners: Simon Starling in 2005, Richard Wright in 2009 and Martin Boyce in 2011.
Other former students include actors Robbie Coltrane and Peter Capaldi, and artist Peter Howson.
The fire in 2014, caused by a faulty projector, destroyed the building's library, which was recognised as being one of the finest examples of art nouveau in the world.
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