An investigator with Ontario's Office of the Fire Marshal says there were no working smoke alarms inside a burning townhome that left four people, including two children, dead in Hamilton overnight.

Investigator Mike Ross told CTV News Toronto that evidence is still being gathered but it appears there were no working alarms in the home at 14 Derby Street, located near Rymal Road East and Upper Gage Avenue.

“We know the fire’s originated on the ground floor -- pretty significant fire spread and fire damage throughout the entire house. Smoke spread throughout the entire house,” Ross said, adding that the cause and where specifically it began on the main floor are still being determined.

Hamilton fire crews responded to the blaze shortly after 11 p.m. on Thursday.

“We had a well-involved fire in a middle unit. We had fire showing both on the front and the back of the unit with heavy smoke,” Hamilton Fire Chief Dave Cunliffe said at the scene.

Hamilton fire also received reports of people trapped on the upper floors.

Crews made entry and began an aggressive search and rescue for the occupants. The fire was subsequently upgraded to a third alarm with approximately 30 firefighters attending the scene at its peak, Cunliffe said.

Two adults and two children were located on the second floor and life-saving measures began.

The four individuals were transported to hospital where they later died from their injuries, Cunliffe said.

“This is absolutely a tragic scene for the family and our heartfelt goes out to all family members that may be involved, especially at this time of year,” he said.

Hamilton police tweeted two other individuals were also transported to hospital with critical injuries. Their conditions are unknown.

No further information about the victims has been released.

Hamilton house fire

Cunliffe said crews were able to get the fire under control within roughly 30 minutes but the home sustained significant damage.

Ontario's Fire Marshal arrived at the scene Friday morning and began their investigation.

They believe the fire started at the back of the first floor and spread inside the home, before combusting and shooting out the back door.

Two townhouse units on both sides of the fire unit were evacuated by crews and residents were allowed to return later in the morning. No other injuries were reported.

Cunliffe added that pet rabbits were found deceased in the fire unit.

A neighbour who identified himself as Chris told CP24 that he saw a child trying to jump to safety.

"It was horrifying, I can't even describe it. Just saw black smoke billowing out of their place and it's just a horrible tragic scene that happened. And when one of them was trying to jump we heard little kids' voices in the background saying 'Save us,'" he said.

"He was trying to jump from the master bathroom suite. So you know, it's a long jump. Neighbours grabbed ladders and that, and thankfully most of the people were saved but not everyone sadly," he added.

On Friday afternoon, Hamilton Mayor Andrea Horwath said her thoughts are with the family’s loved ones and the larger community.

“Absolutely tragic news regarding a fire taking the lives of two adults and two children in a home on Derby Street,” Horwath said.

“Our thoughts are with all their loved ones and the community. I thank our first responders [Hamilton Fire], [Hamilton Paramedics], and [Hamilton Police] who attended the scene and know that this is personally devastating for them as well.”

Cunliffe also commended his crews for going above and beyond to help save the victims.“I just will tell you it's very difficult for the crews when the outcomes turn out like they did but you got to know that they did everything in their power to try and make this a better situation,” he said.