Despite a five-alarm fire at public works in St. Laurent on Wednesday morning, most operations will be up and running on Thursday.

The fire began just before 4 a.m. in the building which contains office space and vehicle garages near Cavendish Blvd. and Poirier Blvd.

"The first arriving vehicles, which were very, very close by, they found three street cleaners on fire in the garage side of the municipal building. The fire spread very quickly into the roof," said Ian Ritchie, operations chief for the Montreal fire department.

Borough Mayor Alan DeSousa said the building holds city trucks, street sweepers, snow blowers and repair equipment, but also assured that most of the damage was to the building itself. Almost all of the equipment was undamaged.

Office workers will be relocated for about a week.

As the sun rose the cloud of smoke coming from the building could be seen for kilometres.

More than 120 firefighters were called to battle the flames as the fire expanded to a five-alarm blaze.

"The problem we're having right now is this building is a cement building structure, but it has a wood structure on the top for the roof, which is a lot of gravel and tar. The fire is in the attic structure between the wood structure and the roof itself," said Ritchie.

He said part of the roof collapsed, but when firefighters made sure the rest of the roof was structurally sound, they were able to get back on the building and fight.

There were also concerns because the building was where all the fluids for the equipment were stored.

“The fire started in the mechanical side of the building. Of course in any garage, there are different flammable liquids. It caused a concern for us as a fire department to ensure that there were no explosions,” said Ritchie.

After four hours firefighters were able to get the fire under control after cutting through the roof to the cement slab underneath.

One firefighter suffered minor injuries and was taken to hospital.

"As soon as the firefighters finish their work the investigators will be able to go inside the building and begin their investigation," said Ritchie.

"Whether it was one of the street cleaners, or something around the street cleaners, that will be determined by our investigators."

The roof suffered the worst of the damage, as did whatever was below and got soaked by water from fire hoses.