Crews have found the bodies of two children at the scene of a row house fire in Oshawa, bringing the number of dead to four, officials said on Tuesday.
The bodies of two men were recovered on Monday evening.
Officials said police will work with Toronto's Centre for Forensic Sciences to confirm the identities of all four people who died in the fire.
Five people escaped from the house after the fire broke out around 1 a.m. on Monday, officials said. The house, believed to be about 100 years old, is on Olive Avenue, near Ritson Road South and Highway 401. Initially, four people were determined to be missing.
"We now have all four accounted for at this time," Oshawa Fire Chief Derrick Clark told reporters near the scene.
Clark said the bodies of the children were discovered on Tuesday afternoon. Officials didn't release their ages, declined to say if they were related to the adults found dead, and didn't say where in the house they were found.
The second and third floors of the house had collapsed and Oshawa Fire Services had to request the help of a specialized team from Toronto Fire Services to sift through the wreckage, Clark added.
Clark acknowledged that finding the bodies of children is difficult for firefighters.
"It's excruciating. This is a tough part of the job but this is the job we do and we are proud to do it and we do it for our communities. We manage to get through these things, but like everyone else, we're human and it takes a toll," he said.
Clark said it's still too early to say exactly where the fire started.
Police investigation to be led by major crimes unit
Const. George Tudos, spokesperson for the Durham Regional Police Service, said the fire has now become a police investigation.
"It is a police investigation led by our major crimes unit," Tudos said. He urged anyone who witnessed anything that may be of interest to investigators to come forward.
Next of kin have been notified.
"We are working with the family. We have notified family members of what we recovered today and sending our condolences to everyone involved," Tudos said.
Ontario's Office of the Fire Marshal (OFM) is helping police and fire services to determine the origin, cause and circumstances of the fire.
"We will assist them in any way we can as far as the investigation goes," said Jim Lawson, operations manager with the OFM.
Earlier, police said seven units on the street were damaged, and four people were taken to hospital. Three of those victims have been released, but one remains there with serious injuries.
Clark said on Tuesday that houses on either side sustained damage.
Tenant tried to rescue others, but blocked by smoke, flames
For tenant Michael Thompson, the fire was a nightmare.
Thompson awoke around 1 a.m. Monday to frantic banging on his door. The Oshawa row house he lived in was going up in flames.
Other tenants who lived on another floor at the residence were yelling that he had to get out.
"We opened the bedroom door, there was so much smoke we couldn't see anything," Thompson told CBC News on Tuesday outside the burned out home.
One unit sustained significant damage.
WATCH | Tenant recounts escape from fire:
Thompson said the smoke was so intense that had to feel his way to the back of the house, where he smashed out a window to get out. His hand was still bandaged after slicing it on the glass.
He said the owner of the home went to the third floor and smashed out two windows for the tenants who lived there, but got no answer.
"They were either overcome by smoke or heat," he said. "There was no answer whatsoever. So they didn't make it out."
'I couldn't help anybody'
Thompson fought back tears when talking about two boys who he also says got trapped in the home. He and their father lost track of them in the chaos, he said.
"By the time we realized they were still in there, the house was engulfed in flames," he said. "The flames were shooting out the windows."
"I couldn't help anybody. That's what's bothering me the most," he said.
Crews are expected to dismantle the wreckage of the row house in the next few days as investigators try to determine the cause of the fire.