A mother and her three children have died after the car they were in was allegedly set on fire by her estranged husband in the Brisbane suburb of Camp Hill.

Key points: Hannah Baxter died in hospital on Wednesday night

Hannah Baxter died in hospital on Wednesday night Rowan Baxter and his three children died in the incident

Rowan Baxter and his three children died in the incident A passer-by tried to help the people in the car escape

Hannah Baxter, 31, was taken to hospital in a critical condition but later died from her injuries.

The couple's three children, aged six, four and three, died in the vehicle, about 8:30am Wednesday.

Ms Baxter's husband, ex-Warriors player Rowan Baxter, died on the footpath near the car with self-inflicted stab wounds after allegedly dousing his family in petrol.

The ABC understands Ms Baxter had jumped from the vehicle at the time and yelled: "He's poured petrol on me".

Detective Inspector Mark Thompson said it was not known if an accelerant was used to start the fire.

The three children of Hannah and Rowan Baxter died in the car fire. ( Facebook )

"We have three deceased children under the age of 10 in the vehicle," he said.



"We have another deceased male, who was known to the children."

Police said their preliminary investigations indicated Ms Baxter was driving the car and Mr Baxter, 42, was in the front passenger seat prior to the incident.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 37 seconds 1 m 37 s Detective Inspector Mark Thompson speaks to media at the scene.

Detective Inspector Thompson said Ms Baxter was taken to hospital with critical injuries, including burns.

"It is a horrific scene," he said.

He said there were "other areas of interest" and anticipated that other crime scenes would be declared.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 24 seconds 24 s Residents reported hearing explosions

"How the fire actually occurred has not been ascertained at the moment.

"For us to call it a murder-suicide or a tragic accident, it's inappropriate for us to try to do that.

"That's exactly what we're investigating, what exactly happened today."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 6 seconds 6 s A car was allegedly set alight in Camp Hill with people inside.

Mr Baxter was a former New Zealand Warriors NRL player.

According to the website of a gym, Mr Baxter ran with his wife at Capalaba, he had more than 20 years experience in the sport and fitness industry.

Passer-by 'tried his best to get to the car'

Queensland Ambulance Service senior operations supervisor Adrian Tong said a passer-by tried to help those in the car escape.

"Somebody did step in to try and help that was close by," Mr Tong said.

"I think he tried his best to get to the car."

Police attend the scene of a car fire, which claimed the lives of multiple people. ( AAP: Dan Peled )

The man received minor burns to his upper body and face that were not life-threatening.

Mr Tong said Ms Baxter had severe burns to a significant part of her body.

"We secured her airway on scene and she was transported, lights and siren, to [hospital]," he said.

Seven ambulances were at the scene as well as more than 30 police officers.

Crews that attended the scene have been stood down and will be debriefed.

"The first crew that arrived on the scene were confronted with a car fire," Mr Tong said.

"We did all we could, but it was confronting."

Flowers and toys were laid in the street where the three children died. ( ABC News: Mark Leonardi )

Camp Hill resident Murray Campbell said he was at home when he heard the car explode.

"I was out the back and came running down the side and … the rest is history," he said.

"Not nice."

Mr Patane said his family was shocked by the incident. ( ABC News: Lexy Hamilton-Smith )

Phil Patane said he raced to the scene to check on his parents, who are residents of the street.

He said they were distressed.

"Oh, it's just devastating, really. You wouldn't think it would happen here in this street."

Authorities on the Camp Hill street where the car was allegedly set alight. ( ABC News: Lexy Hamilton-Smith )

Lachlan Amore, 18, has lived in the area his whole life and said the incident was frightening.

"It's really, really scary. You wouldn't expect it," he said.

"I've been here my whole life and I wouldn't expect anything from here. It's just frightening. Just really frightening."

A house at Carindale registered to the Baxter family has been cordoned off by police as a place of interest.