Firefighters fought back the flames devouring the Spa Le Finlandais for hours, finally extinguishing most of the fire just before 9 a.m.
The majority of the building was destroyed.
A manager at the spa said an internal alarm in the building went off at around 1 a.m. A worker checked around the Labelle Boulevard building and didn't see anything out of the ordinary, she said.
The alarm kept ringing and another employee went to check on the situation. He found the fire burning inside.
"A maintenance man came at 15 minutes before 2 [a.m.] and he went in," Carole Verville told CBC Montreal. "That's how we know that it started in the laundry room."
Around 50 firefighters were called in to extinguish the blaze.
Labelle Boulevard was closed in both directions as emergency crews worked to bring the fire under control. Traffic is still being re-routed around the scene.
The official cause of the fire has not been released.Suggest a correction