Flames ripped through the celebrated Mackintosh building, after it caught fire at around 11.15 p.m., on Friday, the BBC report said.
Nearby buildings, including the Campus nightclub and O2 ABC music venue, were also damaged when the flames spread.
No casualties had been reported.
"A number of engines" were sent to the scene, where more than 60 firefighters were "working hard to extinguish the well-developed" blaze, she 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.
As the fire raged into Saturday morning, witnesses saw it spread to the Campus nightclub and O2 ABC.
The Mackintosh building was completed in 1909 based on designs by Charles Rennie Mackintosh, Scotland's most-lauded designer, the BBC reported.
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.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
