Two people have died in a fire that broke out at a residence in Thornhill Saturday evening.

Fire crews were called to a residence on Conley Street in the area of Steeles Avenue West and Dufferin Street shortly after 7:30 p.m.

Vaughan Fire Chief Andrew Zvanitajs said firefighters encountered heavy smoke in the basement, where they located two occupants.

The male and female victims were pulled out of the home but were pronounced dead at the scene, Zvanitajs said. Both were in their 40s. 

He added that two other occupants of the home were able to get out because of a working smoke alarm on the main floor.

"They saw smoke coming out of a basement register, and they self-evacuated and called 911 from a neighbour's residence," the chief said.

Crews have since put the fire under control. The cause, origin and circumstances of the fire are unknown.

"We will be undertaking an investigation at first light to determine the cause of this fire," the chief said.

Zvanitajs said the Ontario Fire Marshal had been notified about the incident. York Regional Police are also looking into the circumstances surrounding the fatal fire.

When asked if there was a working smoke alarm in the basement, Zvanitajs said a witness informed him that there was.

The chief urged the public to have working smoke and carbon monoxide alarms in their homes.

"That buys you time. And that's the one thing we can't give you. You buy yourself time with a working smoke alarm, and you give yourself that chance to get out," he said.

Meanwhile, Vaughan Mayor Steven Del Duca offered his condolences to those impacted by the fire in a post on social media.

"The effects of events such as this one can be felt by the entire community; our hearts are heavy for the loss of two individuals," Del Duca said.