An off-duty cop has been accused of using excessive force on an Indigenous teenager. 

The officer was filmed pinning a teenage girl to the ground on a Perth train between Joondalup and the City Centre about 4pm on April 12. 

Footage of the incident was captured by the girl's friend who has since posted it to social media and asked others to share it. 

In the video, the 13-year-old can be seen restrained on the ground by the off-duty officer who is on top of her using his thighs to pin her down.

Moments later, the man could be seen picking the girl up and pushing her towards a seat on the carriage, where she looked as if she hit her head on the window.

The man then put his hand on her shoulder and informed the girl that she had been arrested and was 'not obliged to say anything unless you wish to do so'.

During the episode, the girl repeatedly insisted that she was not resisting. 

The state's Public Transport Authority confirmed to news.com.au that the officer was a member of the WA Police Force - and that he claims the girl punched him in the face beforehand.

The girl could be heard asking the officer to stop being so rough as she was being pressed against the train window. 

'F*** off, don't touch me. I'm doing nothing. I'm not f***ing resisting. I'm not resisting,' she said. 

'I'm a 13-year-old girl, and you're gonna do this to me, f*** you, bro. There's kids on here and I get body slammed by a grown man while I'm 13.'

Social media users heavily criticised the officer's decision to get physical with the girl, who they claimed could not properly defend herself. 

'This is the most disgusting behaviour by a so-called police officer! It shows undue force, intimidation, aggression towards a minor, absolutely shocking. I feel for that young girl and hope that police officer’s behaviour is addressed,' one user wrote.

'Shame how this white man thinks he has a right to be standing over and handling a young 13-year-old girl like this. She’s obviously doing nothing and is trying to defend herself. Seriously this s*** needs to stop,' another added.

The incident was allegedly sparked by a robbery which took place earlier when the girl said her cousin was almost robbed. 

In the train, the officer and the girl could be heard arguing about whether or not he did enough to help prevent the alleged robbery. 

Another passenger on the train at the time could be heard shouting out to the off-duty officer that the girl 'was not a threat'.

'From where I was sitting that felt like an unnecessary escalation,' he said. 

The video ends after the train arrived at a station where another police officer boarded the carriage. 

WA Police have since charged the 13-year-old girl with common assault, reports the National Indigenous Times.  

'The officer, who was travelling with family members at the time of the alleged incident, received minor injuries and did not require medical treatment,' a spokesperson said.

'The 13-year-old female was charged with one count of common assault and was issued a juvenile caution.'

Officers are now in the process of reviewing relevant evidentiary material, including Public Transport Authority CCTV, as part of a standard process. 

Anyone with more information about what happened on the train has been urged to contact Crime Stoppers. 

Daily Mail has contacted WA Police and the PTA for further comment.