WA Road Safety Minister Michelle Roberts has labelled an incident where a four-year-old boy clung to a roof rack of a car as it allegedly reached speeds of about 80km/h on a Perth highway as “highly disturbing”.

Mrs Roberts told The West Australian she was unaware of the circumstances of the case but would be seeking a full report from police on what happened.

Officers responded to reports of a young boy on top of a Holden Captiva being driven on Tonkin Highway between Camillo and Harrisdale on Friday about 5.45pm.

The car was stopped at a petrol station on Nicholson Road in Harrisdale where police say three children were in the car with two of them secured in child seats and the third — the four-year-old boy — allegedly unrestrained.

A 36-year-old woman has been charged with dangerous driving in relation to the incident.

Camera Icon A frame grab taken from CCTV footage showing a toddler in the roof rack. Credit: Supplied

Drivers can face fines of $550 and the loss of four demerit points for not making sure a child aged under seven is suitably restrained.

One witness to the incident told The West he saw the car with the boy on top of it on Ranford Road and followed it to Harrisdale about 6pm.

“I beeped the horn a few times and she (the driver) pulled over shortly afterwards near Baker’s House,” he said.

“She looked truly shocked when I told her that her child was on the roof.

“(She) said something about he uses his car seat to climb up there.”

The witness said the woman driving the car got out of the car and pulled the boy from the roof.

“I drove off before I could see him being put back in the car as there was another car behind me,” he said.

Fresh vision of the incident, obtained by Seven News yesterday, showed the boy waving at someone while the car was in motion.

Kyle Jansen, of Harrisdale, was driving home when he captured the baffling scene on video.

Camera Icon Kyle Jansen filmed the incident from the passenger seat of a trailing car. Credit: Seven News

He said an SUV pulled up alongside the car he was in, travelling about 70km/h or 80km/h, when he noticed something moving around on the roof rack.

“I thought it might be a teddy bear or something like that,” Mr Jansen said.

“But as soon as she got right next to me, I noticed a little boy in nappies sitting in the roof rack on top of the car.

“There was another car flashing their lights and hooting. I don’t know how far back they were doing that.”

Mr Jansen said he feared the worst when the car went around a big bend after he followed it along Warton Road.

“He was smiling a lot and laughing, but he was really gripping on,” he said.

“You could see he was really hanging on.

“You could see his weight actually shifted. I’m surprised he didn’t come out. He was just giggling, he was having a ball, (I) don’t know what he was thinking.

“If he came off he would get seriously hurt.

“To not know someone is sitting on your roof is very puzzling.

“People are driving and flashing their lights and hooting — you should just pull over.” Mr Jansen said he had never seen anything like it before.

“I don’t know if I was dreaming or if I was puzzled,” he said.

“I didn’t know what to say.”

Shadow road safety minister Peter Katsambanis said that when he first saw vision of the boy on the car roof rack all he could think was “how did this child manage to survive being on top of a moving car”.

“Laws aren’t going to fix this,” he said.

“We need parents to be aware of their children at all times, particularly when they’re around vehicles.

“The other thing I say is I hope this was just an accident rather than a deliberate act.”