Toronto firefighters have a four-alarm blaze at a building in the heart of Chinatown under control on Wednesday.

Dozens of firefighters were called to the building near Spadina Avenue and Dundas Street West. Toronto Fire said flames were leaping from the two-storey commercial building when crews arrived and there was concern the fire could spread.

At least one firefighter has been hurt during the response, the emergency service tweeted.

Spadina Avenue - 4 Alarm Fire at commercial building, 1 Firefighter injured, no other injuries reported, 17 trucks and 65 <a href="https://twitter.com/hashtag/TorontoFire?src=hash&ref_src=twsrc%5Etfw">#TorontoFire</a> Fighters on scene <a href="https://t.co/CB8YnZCsCk">pic.twitter.com/CB8YnZCsCk</a> —@Toronto_Fire

Toronto Fire Chief Matthew Pegg said the poor weather conditions are making things difficult for firefighters, who have taken a defensive approach, staying outside of the building.

It's unclear what caused the fire, and where in the building it broke out, Pegg said.

"It's very dark and the smoke is thick," he said.

The fire closed the Dundas-Spadina intesection for most of the day, however the roads have now reopened.