Queensland Police have confirmed the 31-year-old mother involved in a fatal vehicle fire at Camp Hill in Brisbane has died from her injuries.
Hannah Baxter died at the Royal Brisbane and Women's Hospital early on Wednesday evening.
Her husband Rowan Baxter died alongside his children Laianah, Aaliyah and Trey on a quiet suburban street in Brisbane's east on Wednesday morning.
Police said it was too early to tell whether it was murder-suicide or an accident, although one witness told News Corp Ms Baxter had run from the car screaming 'he's poured petrol on me."
A member of the New Zealand Warriors NRL squad in the mid-2000s without playing a first grade game, Mr Baxter had until recently ran a Brisbane fitness centre with his wife who was a trampolining champion.
The pair had reportedly separated late last year, and were trying to work out custody arrangements.
However, they were not involved in any proceedings in the Family Court or Federal Court.
Mr Baxter's Facebook profile is littered with pictures of his three children, all aged under 10, along with comments he "loves them to the moon and back" and "daddy misses you all".
Five days ago his friend Joey Abraham wrote under a photo of little Trey: "Chin up brother everything will work out just hang in there my bro alot of people care about you and the situation your facing. (sic)"
Neighbours reported hearing multiple explosions before seeing the car engulfed in flames in Raven Street at Camp Hill about 8.30am.
A man who tried to help at the scene was also taken to hospital with facial burns.
Police will not comment on how the fire started.
"How the fire actually occurred has not been ascertained at the moment, so for us to call it a murder-suicide or a tragic accident, it's inappropriate at this stage," Detective Inspector Mark Thompson said.
"I've seen some horrific scenes - this is up there with some of the best of them.
"It's a terrible thing to be presented with."
Paramedic Adrian Tong said seven vehicles with first-responders and doctors were sent to the scene.
The first crews to arrive were confronted with dead people and the car on fire, he said, but the inferno was put out shortly after.
Neighbour Murray Campbell said he heard a number of loud bangs.
"It sounded very much like a gas cylinder explosion," he told AAP.
He said he called triple zero, and did not see anyone run from the car, which was engulfed in flames.
"It was just horrible, multiple explosions, very loud," he said.
A major crime scene has been established with police cordoning off a large part of the street and several side streets.
The couple's Integr8 fitness website described Ms Hannah as "an enthusiastic, passionate mother of three. Coming from a highly competitive sporting background, Hannah represented Queensland in Trampoline Sports for four consecutive years."
The website said Mr Baxter has trained AFL, Super Rugby and NRL players.
"Rowan and Hannah are top notch athletes with a wealth of knowledge in various areas of fitness," one client wrote on the site..
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Australian Associated Press