40 firefighters were called to the scene on the city’s high street at 1.27am on Tuesday - and were met by a “well developed fire” according to the Scottish Fire and Rescue service.
Police have appealed for any witnesses after the flames seriously damaged the run-down premises above the Old College Bar - regarded as the oldest pub in the city.
Images from the scene showed the bar, a beloved spot for locals that featured in Anthony Bourdain’s Parts Unknown documentary series, remained in tact - although the scale of water and smoke damage to the property remains unclear.
Nine fire appliances and around 40 firefighters were used to bring the blaze under control. Firefighters remained on the scene as of 4pm on Tuesday monitoring for any hotspots.
There were no reports of any injuries.
Detective Constable Neil Bonsor said: “Our enquiries are ongoing into the circumstances surrounding the incident.
“The blaze has caused significant damage to the building’s structure.
“We would urge anyone who was in the area around the time of the incident and who saw any suspicious behaviour to contact us.”
Anyone with information should call Police Scotland on 101, quoting incident number 0119 of May 4 or call Crimestoppers anonymously on 0800 555 111.
Roads in the area, including parts of High Street, Duke Street and West George Street, were closed while emergency services dealt with the incident.
The blaze also temporarily affected train services to High Street, with passengers asked to travel to and from Glasgow Queen Street Low Level on Tuesday morning.
Services to High Street later resumed.
Additional reporting by PA
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