The fire has been upgraded to a five-alarm fire.
Thick black smoke can be seen pouring out of the Bell Media Tower.
Dozens of firefighters are gathered at the Place Montréal Trust complex on the corner of McGill College Avenue and Ste-Catherine Street.
The blaze is believed to be on the roof of the 30-storey building.
Many streets in downtown Montreal are closed due to the fire.
Montreal fire department said on Twitter that it a power failure is possible.
More to follow…