An investigation has begun after a Los Angeles police officer was filmed dragging a woman off the city's subway for refusing to take her feet off the seat.

The incident began when the woman, Bethany Nava, was riding the Metro Red Line train and a police officer enforcing the passenger code of conduct, which prohibits feet on seats, asked her to get off.

At the start of the video, which has now been seen 4.1 million times, the police sergeant can be heard asking the 18-year-old to leave the train and motioning her to stand up.

The officer can be heard saying: 'I already told you what to do and you didn't. You disobeyed me. You're getting off the train.'

He then begins pulling her by the arm, as she begins shouting 'I paid to be on this train' and 'you're pulling me off the train, I can't get my stuff'.

At the start of the video the police officer asks the Bethany Nava to leave the train and eventually begins to pull her arm

As the officer continues to pull her she says 'stop, let me go' before she is eventually dragged off and pinned against the platform wall by the officer.

In the video an agitated Nava shouts at the officer after he lets her go 'I paid to be on this train' and motioned with her foot that she had it on the edge of the seat because it was more comfortable.

'This is not f*****g fair that you took me off the train because I had my foot there because I was comfortable like that,' she said.

'There is no law that tells me that I cannot sit that way because I paid to be in there' but the officer replied: 'It's the rules of the train.'

Meanwhile as small group of bystanders gather, including a woman, later identified by LAPD as 22-year-old Selina Lechuga, who can be heard shouting expletives at the officer.

'Are you f*****g kidding me? You really have nothing to do,' Lechuga says.

The two women continue to remonstrate with the officer on the platform with Lechuga accusing the officer of picking on Nava to meet his monthly arrest quota.

Eventually about half a dozen other officers arrive and Lechuga, who continues swearing, and Nava are both handcuffed and taken into custody.

'This is racism. This is what we are: 2018, m**********s like this want to just try to act like they can do whatever they want. F**k you guys,' said Lechuga, who also appears to spit at an officer.

The 18-year-old high school student is eventually hauled off the train by the LAPD sergeant

A clearly agitated and upset Nava is then pinned to the wall of the station by the officer

The LAPD said it is conducting a use-of-force investigation for Nava's arrest.

Nava's mother told KTLA the high school senior was taken to a hospital with a sprained wrist and her daughter had her heel on the edge of her own seat on the train.

Later Bryant said of the officer he 'was like, you know, you're going to remove your foot or you're getting off the train'.

'He was very agitated. I felt like, when she denied his first request, that was all he needed to hear'.

LA's Mayor Eric Garcetti said investigators are reviewing multiple videos of what happened, the LA Times reported.

'Videos can sometimes tell one picture. We'll have the videos that the officers had as well as the videos that were made.'

Metro's 28 page customer code of conduct states that 'placing feet or shoes on seats or furnishings' is prohibited disorderly conduct, which may be penalized with a warning and/or ejection from the train.