The State Government is refusing to confirm whether four children who died in a fiery crash that is being investigated by homicide detectives were known to the Child Safety Department.

Key points: Homicide detectives are investigating whether the crash was deliberate

Homicide detectives are investigating whether the crash was deliberate The Child Safety Minister says she is legally not allowed to talk about individual cases

The Child Safety Minister says she is legally not allowed to talk about individual cases The Opposition is calling for the Government to be transparent

The crash happened on Monday night when the station wagon their mother Charmaine Harris McLeod was driving collided head-on with a truck on the Bunya Highway at Kumbia.

Ms McLeod, 35, her two sons and a daughter, all aged under six, died at the scene.

Her other daughter, who was aged under 10, died while being flown to Queensland Children's Hospital.

Police Commissioner Ian Stewart confirmed on Friday that homicide detectives were investigating whether the woman deliberately crashed the car.

He said that was why the deaths hadn't yet been added to the national road toll.

Flames hampered bystanders and authorities efforts to reach those trapped in the car. ( AAP: Dan Peled )

"There are very specific rules around traffic crashes that occur when it's not intentional — in other words it's a straight crash."

"But there are very different rules — that's why we now have homicide detectives working on this case — where there is a potential that there is an intention for someone to die.

"So this will take some time and obviously the coroner has a very great interest in the outcome of that investigation.

"But no matter what happened, no matter why it happened it's a tragedy for all of those involved and the Queensland community."

He said the crash was being investigated as a homicide.

Charmaine Harris McLeod was behind the wheel of the car when it hit a truck head-on. ( Facebook )

"Absolutely, we look at all angles and all of that will come out in the wash."

Paramedics described the scene, where people were trapped, as flames engulfed the car as "horrific".

Experienced police officers said it was "catastrophic" and one of the worst accidents they had ever seen.

'Everyone wants answers': Minister

Child Safety Minister Di Farmer said the investigation was a matter for police and for the Coroner.

"I know everyone wants answers and so do I but we need this to be done properly and we need to allow police and the Coroner the time and space to do their job."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 51 seconds 51 s Police responding to fatal head-on crash on Bunya Highway at Kumbia

"The Child Protection Act 1999 prevents me from talking about individual cases.

"However, what I can say is that where a child who is known to the child protection system dies or suffers a serious injury there is a two-tier review process in place to make sure it is thoroughly investigated."

She said the deaths were an absolute tragedy.

"My heart goes out to the family and friends of the McLeod family."

The truck was also engulfed in flames, causing injuries to the driver. ( ABC News )

Deputy Opposition Leader Tim Mander said the deaths raised questions for the government.

"The Palaszczuk government needs to be transparent and open about this case so Queenslanders can have comfort that our vulnerable children are being protected."

"[They] needs to tell us what they knew, when they knew it, and what they tried to do to protect these young children.

"It's absolutely tragic that somebody could get themselves in that situation where it seems they may have taken their own life and the lives of their four children.

"But it's also concerning the reports that this family was known to child protection agencies."

He insisted the Opposition wasn't playing politics with the children's deaths.

"That's not politics — it's about making governments accountable and there have been a long list of issues with regards to protection of children."