A handwritten note found 200metres from the scene of a crash that killed a mother and her four children has prompted police to treat the incident as a murder-suicide.

The note, which is believed to have been written by Charmaine Harris McLeod, 35, was discovered close to the scene of the horror crash, northwest of Brisbane.

Ms McLeod died instantly when the car she was travelling in collided head on with a truck on the Bunya Highway near Kumbia in Queensland, just after 7pm on Monday.

The note, which is believed to have been written by Charmaine Harris McLeod, 35 (pictured), was discovered close to the scene of the horror crash, northwest of Brisbane.

The discovery of the handwritten note down the road from the crash scene (pictured) has prompted police to treat the incident as a murder-suicide

Her children Aaleyn, 6, Matilda, 5, Wyatt, 4 and Zaidok, 2, also perished in the inferno three hours away from their home in Hervey Bay.

While it remains unclear why they were so far from home, the note, along with the absence of skid marks at the scene, resulted in specialist officers and homicide detectives being brought into the case, The Courier Mail reported.

Queensland Police Commissioner Ian Stewart confirmed the crash was 'absolutely' being investigated as a homicide.

He said homicide detectives were working the case as 'there is a potential that there was an intention for someone to die'.

There were no skid marks along the wrong side of the road where Ms McLeod's car hurtled towards the truck that crushed it and killed everyone inside.

Commisioner Stewart said it may take some time to uncover what caused the crash and, for the time being, the deaths haven't been added to the national road toll.

Police also don't know where Ms McLeod was heading when the accident occurred, as the car was travelling south along the highway, about three hours from home.

They believed the family were driving from the Bundaberg area, about 90 minutes north of Hervey Bay.

Superintendent Dave Johnson previously said officers were looking at the case from 'all angles' to determine the exact causative factors.

Police are still working to find out why Charmaine McLeod and her four children (three pictured) were on the Bunya Highway on Monday night, where they all died in a horror crash

Despite being part of a seemingly happy family, Ms Harris McLeod posted comments in online support groups about troubles in her life, including her relationship breakdown.

On one occasion, she wrote about about feeling 'lost and alone', while in another post she replied to a question about items she would rescue from a burning house.

'My children can't be replaced, so I would rescue my children first,' she wrote.

The family is alleged to have also had involvement with the Department of Child Safety, but the department refused to comment on the matter, The Courier Mail reported.

The father of the children and Ms McLeod's ex-partner, James McLeod, said there were no friends or family who lived in that area, and he had no idea why they were there at the time of the crash.

Mr McLeod told Daily Mail Australia on Friday there was a lot about the tragic accident that didn't add up, but he was waiting for police to get to the bottom of it.

'Once the police investigation is done the story is going to explode again,' Mr McLeod said.

Ms McLeod and her children (pictured) died after the car they were travelling in collided head on with a truck on the Bunya Highway near Kumbia in Queensland, just after 7pm on Monday

Detectives say Ms McLeod's car did not leave skidmarks on the highway, south of the turn off to the Bunya mountains, toward Dalby. Pictured: The scene

'I just want to wait for the facts and the police are going to report the facts,' he said.

Initial investigations showed the mother-of-four had tried to overtake a truck by driving on the wrong side of the road when she slammed into a second truck at high speed about 7pm.

The truck Ms McLeod slammed into also caught fire but the driver, a 47-year-old man, escaped the wreckage and was taken to hospital.

He suffered burns to his arms while heroically trying to free the family from the car as it was engulfed in flames.

Three of Ms McLeod's children were unable to be rescued and died in the back seat of the family's station wagon, and a fourth child was rushed to hospital but died on the way.

Supt. Johnson declined to go into detail on the case but revealed specialist detectives had been included in the investigation, and officers were keeping an 'open mind' in their inquiries.

'There's a further investigation involving the positioning of the vehicle and why it was on the road at the time and where it was and what circumstances, if any, are known to police in relation to that matter,' he said.

Charmaine Harris McLeod's children (left to right) Wyatt, 4, Aaleyn, 6, Zaidok, 2, and Matilda, 5, also perished in the fiery crash, which took place three hours away from their home in Hervey Bay

Heartbroken father James McLeod (pictured with his children) on Wednesday recalled the last time he saw his children before the fatal accident, and said he was waiting for police to reveal what had happened to his family

'I understand that there's a range of investigators involved in that matter and we will look at all courses of action and all … avenues as to causal factors.'

Mr McLeod on Wednesday recalled the last time he saw his children before the fatal accident.

The grieving father told The Courier-Mail it was the first time Zaidok told him he loved him.

'Young Zaidok - he was just a little adventurer. A loving and kind kid,' Mr McLeod said.

'The last supervised visitation I had with them, not last Saturday but the Saturday beforehand, he actually said that he loves me, daddy, to me. Just out of the blue.'

Mr McLeod said his youngest was 'an amazing little boy' who was developing well.

He said all his children were 'beautiful souls' who were loved by everyone they met at daycare, church, and school.

'Each of them had their own character. They weren't all the same,' he said.

A family picnic from 2017 with the four children and Ms McLeod's former husband James and sister Katie

Emergency workers described the crash as 'catastrophic' and one of the worst scenes they had ever been to. Police have called in specialist detectives to investigate the circumstances of the crash

Just weeks before the family's tragic death, Ms McLeod claimed she was abandoned by her church when she needed it most.

Ms McLeod attended Bayside Christian Church in Hervey Bay every Sunday for 17 years until she abruptly left, and then explained why in a Facebook post last month.

'I feel as if, if you cant or don't grasp God/healing etc, when they think you should have then you just get left behind,' she wrote.

The single mother said she asked for support after her marriage broke down in early 2018 but got 'very, very little'.

'They were always too busy, not one piece of clothing or a piece of bread was offered, let alone shelter... I feel as if I've done it alone,' she wrote.

'These are the things Jesus did, he ate with the less fortunate. I've asked for prayer before surgery and yes I've had a lot of surgeries, but they don't - they do for others though.'

In the hours after Ms McLeod's death, friends accused Bayside church of failing to help one of its members when she was 'crying out for help'.

'I hope your church reflects on this she is no longer here for you too (sic) help her or her children,' one person wrote.

However, the church insisted it did everything it could to help her and provided many hours of support whenever she needed it.

'People were in contact with Charmaine right up until last week. Our door was always open to Charmaine whenever she needed help and she new that,' it replied.

'Unfortunately, peoples' lives and situations aren't always black and white. We were always reaching out to Charmaine and offering to help as much as she would allow us to.'

Ms McLeod's church, who she blasted in April for their lack of support, dedicated a memorial to the woman and wrote: 'We will miss them all dearly,' on its Facebook page

Charmaine McLeod, 35, died instantly on Monday night when she was overtaking a truck on the Bunya Highway near Kumbia, Queensland, along with her children (three pictured here). A 47-year-old truck driver escaped with minor injuries, but had burns to his arms

Bayside Church said Ms McLeod was a personal friend of many church members who spent time with her during the week to give support.

'We organised professional counseling for her, which she was still regularly attending, we provided meals when needed, looked after her kids, prayed with her many times, visited her at home and the list goes on,' it wrote.

'It's easy to say we could have done more, but honestly we were there for Charmaine when she needed us.

'We are all very sad and hurting with this tragic loss. Charmaine was a wonderful person with four incredible kids.'

Many of the tributes to Ms McLeod that flooded social media on Tuesday and Wednesday highlighted her strong faith.

'Charmaine, you and your children brought so much joy and laughter to our Bayside church community, praying for your family in this difficult time,' one person wrote.

The woman, 35, was driving in South Burnett, Queensland at 7.20pm when she pulled out to overtake a truck. Pictured: The wreckage of the truck

Police have taken further evidence from the scene since the crash which has widened their investigation

Ms McLeod volunteered for charity Youth in Search, which helped at-risk youth - several of whom paid tribute to her after her death.

A fundraiser set up by Ms McLeod's sister Katie Harris to pay for funeral expenses has raised more than $7,000, with the rest to be donated to Youth in Search.

She and her husband moved out of the family home at Howard, west of Hervey Bay, last May and she sold many possessions through Facebook in the months afterwards.

'I've had no issues at all, only moving for family reasons,' she wrote in a post advertising for someone to take over the lease.

Just a few days before the crash she was looking for painting classes in Hervey Bay and surrounds for her eldest daughter Ally.

Friends offered their love and support to Mr McLeod on social media in the aftermath of the tragedy.

Shocked and heartbroken friends in her hometown of Hervey Bay, Queensland, sent tributes in the hours after the catastrophic accident

'James McLeod I am here for you...sorry about your four angels,' a friend wrote.

Friends and family flooded social media with their own tributes to the family, praising her selflessness in looking after her children.

'I've never seen a single mum let alone of four give up so much for their kids,' a friend wrote.

'I can't believe what I've woken up to this never should've f**king happened I'm in so much shock and pain, this is so f**ked life is so unfair'.

'Those kids were something else I tell you and lived like princes and princesses for their short life they had but there was nothing materialistic to it they were just so happy and loved and their happiness came before anything.'

Another friend wrote: 'You were always there for me when i need a friend and you always gave me the kick up the butt I needed. I miss you.'

'You will always be in my heart'.

A neighbour, Gary Loweke, who used to mow the lawn for Ms McLeod said they were a friendly family and the kids were often on the street playing hopscotch or riding their bikes.

'It's a bloody disaster... those four kids waved at us every day as we went past,' Mr Loweke said.

'Charmaine was friendly, she was really nice... she was very good with the kids. If she wasn't there, her sister would be there, but she was never far away from her family for long.

'They'll be greatly missed on the street, all the houses around there had young kids and they all used to play together.

'The littlest fella, he used to just sit there and when he'd see you, he'd stand up where he was and give you the biggest wave. It's hard not seeing that.'