Dozens of Montreal firefighters were busy Thursday afternoon battling a blaze on the corner of St. Denis and de Bellechasse Sts.

It broke out in the back of the three-story residential and commercial building at 6204 St-Denis, sending plumes of thick black smoke into the air.

The building houses a dental clinic on the ground floor and apartments on the upper floors.

Fire officials say 14 people had to clear out of the dental clinic, and that none of the upstairs residents were home.

There's no word yet on a cause.

Photo: Patrick Sansfaçon (La Presse)