About one thousand people are without power after an overnight transformer station fire in North York.

The blaze broke out at a Hydro One facility near Finch Avenue and Signet Drive at around 12:15 a.m.

Toronto Fire says that by the time crews arrived on scene the structure was fully engulfed in flames.

Firefighters were initially instructed not to use flowing water until the power to the transformer station could be shut off. After about 50 minutes, crews from Hydro One did arrive on scene and shut off the power, allowing firefighters to begin pumping water onto the raging blaze.

Toronto Fire says that the facility was also a significant distance from hydrants, which further complicated matters.

They say that at one point crews ran out of hose and had to find a workaround to get water on the fire.

During the height of the fire, police closed down Highway 400 from highways 407 to 401 as well as Finch Avenue from Weston Road to Highway 400 and Signet Drive from Finch Avenue to High Meadow Place. Highway 400 and Finch Avenue have since reopened, however.

Public works crews with a vacuum truck were also called in to assist with the cleanup after the transformer began to release oil.

By about 3:40 a.m. the majority of the blaze had been knocked down but Toronto Fire says that crews do remain on scene and are spraying water on a transformer to cool the oil inside, which has overheated.

“We will be here until the transformer itself is cooled to the point that it is safe and that is an ongoing process. It could be up to a day, at least,” District Chief John Walsh told CP24 at the scene.

Up to 35,000 customers were without power

According to Toronto Hydro, there were as many as 35,000 customers without power at the height of the outage though that number was reduced to 7,000 by early Saturday morning. Toronto Hydro was then able to restore power to another 4,000 customers by 2 p.m. on Saturday, leaving about 3,000 in the dark. By 3:45 p.m., only one thousand customers were in the dark.

Toronto Hydro says that the remaining affected customers could be without power for “quite some time.”

“Our crews in our control room did a really great job of redistributing power and rerouting it in order to bring back our customers even without this issue being resolved. They sort of worked some magic in the control room by doing some switching but these remaining 7,000 customers may be out for quite some time,” Toronto Hydro Spokesperson Tori Gass told CP24 on Saturday morning. “We have to be careful and mindful of overloading that system.”

The outage is affecting customers in an area bounded by Steeles Avenue to the north, Highway 401 to the south, Kipling Avenue in the west and Dufferin Street in the east.

Toronto Hydro is asking customers in that area to “reduce their electricity use to prevent overloading the system.”

Toronto Fire says that the Ministry of Environment has been notified.

Pearson International Airport was also warned about the potential for heavy smoke while the blaze was still not under control.

No timeline has been provided for the full restoration of power.