Authorities are investigating after fake Chinese police cars were spotted in Adelaide and Perth amid pro-Hong Kong demonstrations across Australia, but the owner of one of the cars has told police it was a "joke".

Key points: Police in SA and WA have confirmed sightings of cars with Chinese police markings

Police in SA and WA have confirmed sightings of cars with Chinese police markings It comes as local demonstrations over the situation in Hong Kong escalate

It comes as local demonstrations over the situation in Hong Kong escalate WA Police said the owner of one car had been spoken to and removed the insignia

In South Australia photos have surfaced of a car — bearing Chinese characters — parked at various spots around Adelaide's CBD.

SA Police told the ABC it was aware of the vehicle's current location and was investigating if it has been involved in any offences.

Police in Western Australia also confirmed they had received reports of a car with Chinese police markings.

"WA Police spoke to the driver of the vehicle who stated he purchased the decals online," a spokesperson said.

"He placed them on his car as a joke and after being spoken to by police has taken them off the vehicle."

The sightings follow rallies around Australia in support of Hong Kong's pro-democracy demonstrators, with an event in Melbourne turning violent.

On Sunday, about 100 pro-Hong Kong protesters clashed with pro-China activists in Adelaide's Rundle Mall.

The car was sighted at several spots around Adelaide. ( Supplied )

The organiser of that rally, who goes by the pseudonym Charlotte, said she had heard reports about the police car, but was unclear about the owner's motivations.

"There are people who feel intimidated by it … to be honest, I don't really know what to make of it. I think it's highly inappropriate, especially when you pretend to represent a foreign law enforcement unit in a Western country," she said.

"Initially we thought it was a bit of a joke. We did receive reports of it a few days before our protest.

"Since this morning, I was told there was actually another one that started first in Perth, so now we are starting to get a bit concerned.

"Could this be an organised effort by the Chinese Government or is it really just two completely separate instances of a prank?"

Charlotte (not her real name) said she wants to remain anonymous to protect her family. ( ABC News: Claire Campbell )

Greens call for police impersonation ban

SA Premier Steven Marshall described it as "quite a curious situation" but said police were investigating.

"My understanding is that the police are doing an investigation, they've been able to identify the vehicle, now they're trying to figure out whether there has been any breach of any of the existing laws," he told ABC Radio Adelaide.

"Of course, it's illegal to impersonate a police officer in South Australia, so the police are now conducting that investigation to see whether or not a breach of the state laws has occurred."

A Chinese police car in Shanghai with the markings of China's Ministry of Public Security. ( Wikimedia Commons: Navigator 84 )

Greens MP Tammy Franks said legislation needed to be tightened to prevent people from impersonating foreign police in Australia.

"It appears that our laws anticipate perhaps somebody impersonating an Australian police car but certainly not a Chinese cop car on the streets of Adelaide," she said.

Ms Franks said the police car was "potentially intimidating and threatening, particularly ex-pats from China or people from Hong Kong and Taiwan".

She said she would introduce a private member's bill to "ensure impersonating police forces is illegal in South Australia and send a clear and strong message that we stand for peaceful protest and democracy".

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 22 seconds 1 m 22 s Pro-Hong Kong and pro-Beijing protesters clash in Adelaide.

Foreign affairs commentator Keith Suter said while the car appeared to be "fake", he was concerned about the presence of Chinese agents infiltrating the protests in Australia.

"It has no jurisdiction in Australia, but there certainly is an issue of the Chinese Government having its students spy on other students to make sure they're not supporting the protests," he said.

'Our loved ones can become endangered'

Charlotte, who said she wanted to remain anonymous to protect herself and her family in Hong Kong, said protesters had received threats from pro-Chinese elements online.

"It's not like we are hiding our identity because we have something to hide. It's more so because if we get found out … our loved ones or even ourselves can become endangered," she said.

"There are reports of people who haven't worn a mask being identified online, and they have been tracked down."

A pro-democracy protester in Adelaide shows solidarity with Hong Kong. ( ABC News: Lincoln Rothall )

Charlotte said her brother — who was recently in Hong Kong — had recently been involved in a peaceful protest that suddenly turned violent.

"It was completely peaceful, absolutely fine," she said.

"The riot police showed up and then they started chanting and they started raising flags saying they were going to deploy tear gas and other weapons.

"What happened was — it was basically like Moses and the Red Sea. The crowd just split."

Mr Marshall said he was "very concerned" by the situation in Hong Kong.

"We're very concerned whenever there are protests like this, we have been seeing the fairly graphic images on our television now for a week regarding protests in Hong Kong," the SA Premier said.

"We just hope those protests and the situation in Hong Kong can be resolved peacefully."