Almost 170 firefighters battled a rare seven-alarm blaze that started inside a century-old downtown Toronto paint store early Friday morning.

The fire began at 2 a.m. and engulfed the Ontario Paint and Wallpaper business at 175 Queen St., just east of Sherbourne Street, before spreading to two adjacent buildings.

Flames shot into the night sky and across Queen, and the thick, toxic smoke forced the evacuation of dozens of residents in nearby apartments.

Fire officials closed off an area from Sherbourne east to Parliament Street.

Toronto Transit Commission service was re-routed onto King Street, and officials expected the public transit system to be disrupted for most of the day.

Fire crews used nearly 100 pieces of equipment before the flames finally disappeared at about 8 a.m., nearly six hours after the fire began.

"This was a very fierce fire," Division Commander Ron Jenkins told CTV, noting it was one of the largest blazes he has ever battled.

"Seven-alarm fires don't happen very often in this city, and our concern was that this fire could definitely spread to other places."

No one was hurt, except for a firefighter who injured his leg falling off a ladder.

TTC buses were called to the scene, and evacuated residents were loaded onto them to keep warm.

The family-owned paint business has been operating since 1913, and two other damaged buildings are equally as old.

The owner of the paint store told Jenkins he could not believe what had happened. He said the three-storey building had recently undergone extensive renovations.

The structures had a shared basement, which may have contributed to the fire's spread, CTV's MairiAnna Bachynsky reported from the scene.

Officials labelled the fire seven-alarm because it was a large blaze, inside a large building that carried many hazards.

Residents living in nearby apartments who were evacuated were thankful to have escaped unharmed.

The timing couldn't have been worse, however, for one couple who is getting married in two weeks.

"It was pretty overwhelming. It didn't really sink in until I actually saw the damage and realized that everything was gone," said bride-to-be Amber Wilson, fighting back tears.

The cause of the blaze is not yet known.

The Ontario Fire Marshal's office is investigating.