The Ontario Fire Marshal is investigating after a fire damaged an industrial building with a basement medical marijuana grow-op early Saturday morning.

Firefighters were called to the upholstery factory, near the corner of Dupont Street and Westmoreland Avenue in Dovercourt, shortly before 10 a.m. They were alerted by employees who had arrived to begin their morning shifts.

According to Platoon Chief Trevor Trotter, the two-alarm fire had broken out on the first floor but was quickly knocked down by the first crew to arrive. All of the workers were safely escorted out of the building and no one was injured.

Firefighters searching the building found a medical marijuana grow-op in the basement. Police were called to the scene and it was determined that while it was a legal operation, the licence holder may have been growing more plants than his licence allowed for.

Staff Sgt. Steve French of Toronto Police Services 14 Division told CBC News it 'appeared evident' that the operation exceeded the licence limit. Police, however, were not able to begin looking into the circumstances of the grow-op until the fire marshal's office had completed its own investigation of the blaze, he added.

If the grow-op was in violation of the licence, it would likely remain a "regulatory matter" and not a criminal investigation, according to French.

Trotter said earlier Saturday that it did not initially appear that the fire was related to the grow-op.

Roads in the area were briefly closed as fire and police officials investigated, but have since reopened.