A one-alarm fire that broke out at Old City Hall on Monday night may have been deliberately set, Toronto police said.

Emergency crews were called to the historic building, located in the area of Queen and Bay streets, at around 8 p.m.

At the time, Toronto Fire said there was a fair bit of smoke visible in the area and a significant amount of water damage caused by sprinklers going off inside the building.

Speaking with CP24 at the scene, Toronto Fire Chief Matthew Pegg said the fire is being considered suspicious in nature.

“We received a report for a fire alarm activation in this building,” he said. “Our crews arrived, there was nothing visible from outside and in accordance with normal protocol they made access into the building to check and very shortly after confirmed there was a working fire in the south-east corner of the building.

Officers said the fire was extinguished at around 10 p.m.

No injuries have been reported.

In a tweet, Mayor John Tory thanked Toronto Fire for their "quick response."

An investigation into the incident is underway.