A young child has died and six family members have been injured, including three in life-threatening conditions, in a ferocious house fire.

The house on Merritt St in Harristown, Toowoomba, became engulfed in flames about 12.30am on Wednesday.

WATCH THE VIDEO ABOVE: Deadly Toowoomba house fire.

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Police say six people were able to escape as the fire took hold, including a 34-year-old man, a 36-year-old woman and four children.

A fifth child did not make it out of the house and was missing for some time.

Later on Wednesday morning Queensland Fire Department station manager Neil Goodman confirmed a body had been found.

“Once (crews) could bring the fire under control sufficiently, just near the front door they located one (deceased person),” he said.

The police later said it is believed to be a nine-year-old boy, however formal identification is yet to be completed.

Goodman said crews who arrived at the scene first were greeted by a “wall of flame and heavy smoke”.

The front area of the house was mostly impacted.

“The guys had quite ... a difficult time making access and getting in to conduct a primary search,” Goodman said.

He said he spoke to one of the family members who was “hysterical” and told crews where the missing child might be.

“We’re all fathers, we’ve all got children, so its aways hard, it’s a little bit harder when it’s sort of similar to your own situation,” Goodman said.

The 36-year-old woman was airlifted to Royal Brisbane Women’s Hospital with serious injuries where she remains in a critical condition under police guard, Queensland Police Service (QPS) said.

A four-year-old girl and seven-year-old girl were airlifted to the Queensland Children’s Hospital where they remain in a critical condition.

A 34-year-old man was taken to Toowoomba Base Hospital with serious injuries and remains in a stable condition.

An 18-year-old was also transported to the hospital and treated for non-life-threatening injuries.

An 11-year-old boy involved in the incident was uninjured.

Neighbour Jennifer Smith described the blaze as “intense”.

“Little children were burnt and they were taken away in the ambulance,” she told 7NEWS.

“It was bright orange along here from my bedroom window, it was very close to the fence line.”

She said the family were always friendly and the children often played in the front yard.

“They usually wave to me when I’m leaving,” she said.

Acting Superintendent Scott Stahlhut said investigations into the cause of the fire are ongoing.

“We are in the early stages and working closely with forensics and scientific teams to get a clear picture of what happened,” he said.

Stahlhut said police are not yet in a position to confirm the relationships between those inside the home.

“We’re still working through that information to determine the status of the relationships at the address,” he said.

They are also not ruling anything out as they continue to investigate whether the fire may have been suspicious.

Police said that the house remains a crime scene and is currently undergoing forensic examination with the assistance of the Homicide Investigation Unit.

They confirmed they are currently not looking for anyone else in connection with the incident.

“We are deeply saddened by this incident,” Stahlhut said.

“Our hearts go out to the Toowoomba community and to the family and friends involved.”

Anyone who has any information or relevant dashcam or CCTV vision has been urged to come forward.