Police are considering whether to charge a Perth mother spotted driving on Tonkin Highway with her four-year-old son riding on the car's roof rack.

The sight stunned other drivers who tried to stop her and raised the alarm, worried the boy might not be able to hold on.

New pictures obtained by Seven News captured the moment the SUV took a sharp turn with the toddler still on board.

Witnesses, including Kyle Jansen, were left gobsmacked.

"He was just sort of gripping on,” Mr Jansen said.

“You could see him move from the one side and come back. But he was just giggling. He was having a ball. Yeah, I couldn't believe it.

Camera Icon Kyle Jansen filmed the boy’s wild ride from the passenger seat. Credit: Seven News

He first thought the little boy was a teddy bear strapped to the roof.

Mr Jansen spotted the toddler on Ballanup Road in Harrisdale.

Police say the toddler's wild ride spanned five suburbs, an area of about 11 kilometres.

It included Ranford Road and Tonkin Highway, where the speed limit is 100 kilometres an hour.

Other witnesses told Seven News they spotted the SUV on Wright Road, Reilly Road and Balfour Street.

It was eventually stopped at a service station, the driver questioned by police. -

Seven News has been told they're still considering whether to lay charges.

Camera Icon Police are considering laying charges. Credit: Seven News

While the boy was on the roof of the Holden Captiva, police say two other children were inside the car and strapped into child seats.

A $550 fine and 4 demerit points is the penalty for not properly restraining a child under seven years of age.

The mother allegedly told one bystander the boy “climbs up there using his car seat sometimes".