The streets around the scene were quickly cordoned off by police as huge numbers of people gathered to watch the fire quickly spread to the roof of commercial premises on the street.
Workers from nearby shops, cafes and banks were evacuated by the emergency services over fears the fire could spread further.
“When I first arrived I saw smoke emerging from the Victorian building above the Holland and Barrett and the Newsagents, it started around quarter to 9 and just got worse from there,” said Marion Reid, 52, who arrived at the scene just as the blaze began.
Around 11am, Eren Karaman, 32, was evacuated from the nearby Pret A Manger as police extended the cordon down to West Nile Street.
He said: “Smoke was everywhere and the street had already been closed up next to the Burger King, after 20 minutes the police decided to shut our side of the street and we had to evacuate the building.
“We’ve been told that it is likely to be shut today and possibly tomorrow and now we are just waiting to see what will happen.”
David McKenna, 27, was on his way to start his shift in The Works when he popped into Greggs for a coffee.
He told The Scotsman: “I saw the fire engines down the alleyway and I remember thinking that I hoped that it wasn’t our shop, I saw the smoke but didn’t think it was anything that was going to be too serious.
“I went into Greggs and as soon as I got to the counter the police came in and evacuated the shop. We were standing outside The Works originally but then they moved us down to Lauders, then they moved us to the Bank of Scotland and finally West Nile Street. Flames have completely engulfed the building, the whole building is old and in a state of disrepair.”
One other witness, who asked not to be named said that if you didn’t know any better you would “think they were filming a war movie in the city.”
As the morning progressed, other nearby buildings were evacuated. Twitter user David Farrell posted: “We were evacuated from the Herald Building in Glasgow due to the fire. Air was NASTY. Had bits of soot stuck on clothes almost immediately.”
While another user Cj added a video showing the fire on the roof and stated: “Big big flames... fire looks to have jumped buildings from where it started from... Sauchiehall Street is a no-go today...”