A fire that took nearly 10 hours to extinguish in downtown Kitchener was set by people who were homeless trying to keep warm, according to fire officials.

Crews were called out around 1:30 a.m. to he former Trinity United Church on Frederick Street.

Kitchener Fire Platoon Chief Terry Gitzel said the fire was in a difficult part of the building to reach, and it wasn't extinguished until 10 a.m.

The fire was immediately deemed suspicious because the building was in the process of being demolished and power had already been cut off.

By noon on Thursday, fire officials said they believe the blaze was caused by people who are homeless trying to keep warm in the structure.

Kitchener, Ont. crews have put out the fire at the former Trinity United Church at 74 Frederick Street, Thursday Nov. 15, 2018. (Gary Graves/CBC)

Fire officials believe the fire grew out of control and that it was accidental.

Six people were inside an attached portion of the building when the fire started, and all got out safely, fire officials said.

Overflow shelters near capacity

The YWCA Emergency Shelter next door had to be evacuated during the fire. More than 100 people were moved around the corner to St. Andrew's Church. They were able to return to the shelter after breakfast.

CEO Elizabeth Clarke said staff at the shelter were aware that people were sleeping in the empty building.

"It's not at all an unusual situation. Our administration office is in the downtown, just a block away and we have people sleeping in our underground parking lot at night. I think everywhere there are people who are sleeping rough," said Clarke, who is also a Region of Waterloo councillor. "When there's an empty building, that's a very inviting place to go. It's private, and it's sheltered, and you can come and go."

She said their women's shelter has been over capacity since the fall, and their emergency overflow shelter has been near capacity in recent weeks.

"Our biggest concern is that between the fire department and the owner of the building that something be put in place to ensure that people aren't staying there and this doesn't happen again because it could have been more serious," said Clarke.

"This was just property damage but our fear is that it will be something worse next time."

City crews remain at scene

The area remains closed to traffic while city crews work.

"There's a lot of water on the ground that's turned to ice, so it'll be very slippery. So if people can avoid that area it would be very good for them," Gitzel said.

Waterloo Regional Police Service said the damage is estimated at $100,000, though the building was in the process of being torn down.