Fire chiefs believe restoration work at Glasgow School of Art has been "destroyed" after a second huge blaze in just four years.

Flames ripped through the Mackintosh Building late on Friday night and into the early hours of Saturday morning, with smoke seen for miles.

Around 50 firefighters remain at the scene of the blaze, which has been described as "contained".

The art school and nearby nightclubs have been "extensively damaged", the Scottish Fire and Rescue Service said.

Footage showed the O2 ABC venue on Sauchiehall street engulfed in flames.

No casualties have yet been reported, but local residents have been evacuated and may not return to their homes until later today.

Work was ongoing to return the famous building to its former glory after a devastating fire in 2014, which resulted in the loss of the celebrated Mackintosh Library.

But Scottish Fire and Rescue Service deputy assistant chief officer Peter Heath said he believed the restoration - projected to cost between £20m and £35m - had been destroyed.

First Minister Nicola Sturgeon praised the emergency services for their response.

She 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.

"First and foremost my thoughts are for the safety of people. At this stage it appears there are no casualties and I hope that continues to be the case.

"The professionalism and bravery of the fire service, and the rest of the emergency services, was once again demonstrated last night.

"This is clearly an extremely complex and large-scale incident, and one that is ongoing. I would like to thank the emergency services for their continued efforts."

Witnesses said they believed the fire was worse than the previous blaze four years ago.

Asked if the restoration work had been destroyed, Mr Heath replied: "I would say, given the extent of the fire, that would be a fair comment."

A number of roads remain closed in Glasgow city centre, while fire crews are pumping water from the River Clyde.

The Scottish Fire and Rescue Service's area manager David Young is the officer in charge of the incident.

He said: "The fire has now largely been contained but this remains a protracted incident and our efforts very much continue at this stage to extinguish the fire and ensure the community is protected.

"There will be disruption around Dalhousie Street, Sauchiehall Street and Renfrew Street and I would advise the public to avoid these areas at this present time.

"I would like to thank our firefighters on the ground and our Operations Control firefighters for working effectively with our partners throughout the night and into today."

Police Scotland said: "Officers remain at the scene of the major fire in Glasgow city centre.

"A high volume water pump from the River Clyde has been put in place by the Scottish Fire and Rescue Service, which has resulted in a number of closures on the following roads: Broomielaw Brown Street Argyle Street Douglas Street Dalhousie Street

"Closures also remain in place around the Sauchiehall Street area."

Stuart Robertson, director of the Charles Rennie Mackintosh Society, said the fire was "terrible" and a "massive body blow" and would be "sending shock waves around the world".

He said: "This is a world-class building. With all the restoration work going on it's just horrendous, I can't really believe it.

"I've only seen glimpses, and what the firemen are saying, reading between the lines it looks bad. The last time they stopped it going into the east wing this time it looks as though it's gone from the east wing all the way through.

"To see some of the work and the beautiful craftsmanship that's gone on and I'd seen a glimpse of the new library taking shape and the studio work and all the painstaking work that's gone into the restoration is just . . . people must feel sick."

Alan Dunlop, professor of architecture at the art school, said he was "devastated".

He said: "It's horrible. The building does look as though from the inside it's been totally gutted. All that seems to remain is the stone walls on the outside.

"The deeply sad thing is that yesterday was graduation day. So the students will have felt elated and very happy, and then to wake up the next morning they will be very sad indeed."