Working since early Monday morning, firefighters continue to battle a stubborn five-alarm blaze at a self-storage facility in the Junction.

Crews were called to the scene at Save and Secure Self Storage at the corner of Pelham Avenue and Osler Street — in the Dundas and Dupont area — around 6:15 a.m. Monday.

Heavy smoke caused traffic disruptions during the morning rush and prompted evacuations of neighbouring homes and an elementary school. Some trains were also diverted.

Toronto Fire district chief Stephan Powell told CityNews crews were forced out of the structure after concerns of a possible collapse.

Fire crews later went back in but a scary incident forced a second evacuation when a firefighter suffered minor injuries falling between the second and third floors. The concrete floor gave way after becoming weakened by the flames and intense heat.

"The floor gave way and the firefighter, I'm told, went through the floor to the second and was onto the debris," said Fire Chief Bill Stewart.

The fight to extinguish the blaze has been a challenging one from the start. As many as 80 firefighters rushed to the scene and had to haul hoses from quite a distance because of train tracks to the south and west of the building, Powell said.

The facility had sprinklers but Powell said he wasn’t certain if they were working.

One of the major challenges firefighters are facing is the unknown — crews have no idea what people have stored in their units.

“We’re not quite sure what we’ve got in there but we’re working to try and identify who’s got units in there,” Toronto Police Sgt. Stella Karras said.

Firefighters were presented with other challenges including access problems and the burning of debris that required the use a wetting agent.

Officials haven’t been able to get a hold of the building’s owner and are still trying to determine the cause of the fire. Firefighters had to use saws to cut through some ground-level steel doors in order to get water into the building.

Although it's early, officials tell CityNews the initial damage estimate is at least $1 million.

Some homes on Pelham have been evacuated as a precaution, and owners still have not been allowed to return. St. Josaphat Catholic School, also on Pelham, was also evacuated. The students were moved to St. Luigi Catholic School on Ruskin Avenue. The school will remain closed on Tuesday as a precaution.

Osler, Pelham and Uxbridge were closed to traffic and police urged people to avoid the area.

GO Transit suspended service on the Kitchener line because of the fire, but it has since resumed, the transit authority said.