About 100 firefighters spent Thursday afternoon battling a stubborn fire on St. Hubert, which was still raging six hours after it sprouted up up in a ground-floor commercial unit at about 11 a.m.

Heavy smoke and the possibility of structural collapse prevented firefighters from penetrating far inside the structure, which houses a clothing store along the popular shopping strip.

The cause of the blaze remains unknown but it coincided with a pipe defrosting operation.

Firefighters were still on the scene at 5 p.m. battling the fire which forced the closure of the street between Beaubien and St. Zotique.

At 10 p.m. Montreal fire authorities tweeted that there were still 60 firefighters on site.

Police estimated the damage to be around $1.5 million.