Four members of the same family -- two children, their mother and their 83-year-old grandmother -- are dead after a fire ravaged their Port Colborne home in the early morning hours of Wednesday.

The fire broke out at a house on Nickel Street East shortly before 1:30 a.m.

When emergency crews arrived on scene, they found the house engulfed in flames.

An 83-year-old woman identified as Eva by neighbour and family friend Adrienne Gary was pronounced dead at the scene and police say they believe 37-year-old Tammy Burd, her two-year-old son Josh and her 15-year-old daughter Sam were also killed in the fire.

Firefighters were initially able to enter the house and when they got inside, they found the elderly woman collapsed near the front of the home.

Attempts to resuscitate the 83-year-old woman were unsuccessful and she was pronounced dead at the scene. A post-mortem examination is scheduled for today.

"At this point, a 15-year-old female, a two-year-old boy and a 37-year-old woman remain unaccounted for and we believe they're still in the residence," Niagara Regional Police Const. Phil Gavin told CP24 Wednesday morning. "It's our understanding that they're from the same family."

He said Burd’s husband and another male family member -- believed to be an uncle -- were able to escape the blaze.

The structural damage caused to the home by the fire has posed "a challenge" for emergency crews trying to get into the building and locate the remaining occupants.

Gavin said that part of the second floor of the building has fallen onto the first floor and that the roof has collapsed.

“My understanding is that the flames were pretty intense when they (firefighters) got here. They certainly made the rescue attempt. They removed one female and further attempts were beaten back by the fire," he said.

Port Colborne Fire Chief Thomas Cartwright told reporters at the scene that fire crews haven't yet started a full investigation into the cause of the fire as the building is still considered unsafe.

"I can tell you this, I've been in this job for almost 45 years. In those 45 years, up until today, I've had four fire deaths. I've had four today in total, so that tells you how serious this is," he said.

"It really is difficult to understand why this happens… obviously this time of year is very devastating. I’m concerned about my people. My emotions speak from myself," Cartwright said, holding back tears.

“We hope we’re never needed but it obviously happens.”

Liz Winger, who identified herself to reporters as Burd’s aunt, said her family plans to cancel Christmas in light of the horrific tragedy.

"We’re not even going to be celebrating Christmas. We can’t. It is just too hard," Winger said.

Neighbours previously told CP24 that a mother and her two children lived in the home along with the children's great-grandmother. An officer at the scene told reporters that police couldn’t confirm how the woman was related to the family.

"She was so nice, so kind. When I used to see her outside in the summertime on the porch, she was so nice," one neighbour said of the elderly woman killed in the fire.

"I cannot believe this at all. This is a shock to me."

Melvin Smith said he woke up Wednesday morning to "red lights flashing through his window." He said the family were "very nice people."

"They were loving and caring. It’s a sad, sad day... a very sad day,” he said.

The coroner and investigators with the Fire Marshal’s Office are now on scene.

Speaking to reporters Wednesday afternoon, Ontario Fire Marshal Ross Nichols said special equipment will be brought in to help stabilize the "structurally unsound" building and aid OFM investigators in combing the charred scene.

“It’s far too early (to speculate) in any substantive way. We’ll have to wait for the investigators to follow the science and have it play out to get all the circumstances,” Nichols said. "It will be challenging, of course, as the temperature drops and visibility is limited not only due to blizzard-like conditions but due to fading light. It will present the investigators with some challenges... (but) the OFM investigators are among the best there are and they can pull apart a scene like this."

Nichols called the tragedy "an incredible loss" for not only the community but for the first responders who attended the scene.

At the height of the fire, officials from Port Colborne Fire Services, Niagara Regional Police, Niagara EMS, and Welland Fire Services were on scene.

The cause of the blaze has not yet been determined and it is not clear if the home had working smoke detectors.

“We’ll be looking for origin, cause, circumstances and (we will be) paying particular attention to whether there were working smoke alarms inside the residence,” Nichols said.