West Australian Police are conducting an internal investigation into the actions of officers after a bystander filmed an 18-year-old man being hit by a police car and injured in the south-eastern Perth suburb of Thornlie.

Video posted to social media shows the man walking along Wilfred Road when an unmarked white police SUV with its emergency lights on swerves in front of him. He is next seen lying on the ground.

Local residents who witnessed the incident on the weekend have offered differing opinions on whether or not they think police acted deliberately.

Mervyn Eades from the Deaths in Custody Watch Committee said the actions of the police involved were excessive. ( ABC News: Nicolas Perpitch )

Mervyn Eades, from the Deaths in Custody Watch Committee, was sent the video and posted it to Facebook. He said it was excessive and the young Nyoongar man had bruises on his lower back and would be undergoing a CT scan.

But in a statement, police said the man was being sought for questioning over a telephone complaint of suspicious activity in the area.

The statement said officers found the man at 2.23pm and "a scuffle ensued where one officer was injured", before the man fled "and was arrested a short time later on Wilfred Road after colliding with a police vehicle involved in the search."

At least two ambulances were called to the scene and the man was taken to Fiona Stanley Hospital for treatment.

Police Minister Michelle Roberts said she was troubled by the incident.

"On the face of it, it's very disturbing and appears to be quite unacceptable," she said.

"So the officers involved will be interviewed by professional standards and a full report done."

Chase witnesses offer differing perspectives

Local residents Dirk Jagers and Kevin (who did not want his surname used), said the man and a female friend had knocked on their doors asking them to call a cab.

Mr Jagers said he went inside to call a taxi, but when he came back out the unmarked police car had pulled into his driveway and the young man ran up the street.

Wilfred Road resident Dirk Jagers said he believed police had deliberately run the man down. ( ABC News: Nicolas Perpitch )

The neighbours said they saw the two police officers fall over as they gave chase on foot, but they caught hold of the man at a nearby roundabout and put one handcuff on him, before he again escaped.

Mr Jagers said one officer then gave chase in the unmarked car, and it was directly across the road from his Wilfred Road home that the man was struck.

"[The police officer] raced up to the corner. And, as far as I'm concerned, he ran him over," Mr Jagers said.

"He deliberately knocked him on to the ground, and I don't think it was right."

But Kevin saw the incident differently.

Thornlie man Kevin, who did not want his surname used, said police did not appear to intentionally hit the man with their car. ( ABC News: Nicolas Perpitch )

"I saw an unmarked police car with lights on sort of swerve in front of him to block his path. He sort of changed direction and the police car hit him, or nudged him or knocked him," Kevin said.

"In my mind, it wasn't intentional by the police to try and hit him.

"They were just purely trying to stop him from fleeing."

Mr Eades said police should arrest Aboriginal people in the same way they arrested everyone else.

"Police arresting and apprehending people in that manner, it should not be tolerated," he said.

"You know, enough is enough. Our boys are in danger."

The internal investigation will examine all the circumstances around the way the officers went about arresting the man.