There were chaotic scenes as residents were evacuated from properties in Baliol Street following the incident at lunchtime yesterday.
Families had to hurriedly leave their homes, many clutching their pets, after being told to move out immediately.
Emergency services were called to reports of a roof collapse but local residents and shopkeepers then smelled gas. It is unclear whether the smell was related to the cause of the collapse or as a result of a damaged pipeline following the incident.
One evacuated resident said: "I was asleep and woke up when I heard this loud crash. I knew it didn't sound good, but I can't believe the roof is gone.
"We were told it's gas and that's why we can't get back in yet.
"We have no idea when we'll be able to go home."
No-one was injured, but masonry was scattered around the street.
Another neighbour added: "Everyone came out the shops and flats to see what was going on and there was a strong smell of gas. I couldn't believe how much damage has been done.
"We're lucky no-one was walking in or out of the building when it happened."
Fire crews, including specialists officers, were at the scene assessing the damage and ensuring the building was safe.