Police say they have launched two separate investigations after allegations of police brutality at Sydney's Mardi Gras celebrations.

A video posted on YouTube shows a policeman throwing the handcuffed 18-year-old to the ground and putting a foot into his back after the parade on Oxford Street on Saturday night.

The young man appears to have a head injury, and an officer repeatedly tells witnesses to stop filming as the man cries and cowers on the ground.

What happened between police and the man before the incident is not clear.

Assistant Police Commissioner Mark Murdoch says that confrontation, at 10:00pm, and another incident at 11:30pm are now being examined.

"Both investigations have been referred to the Professional Standards Command who will conduct a thorough, professional investigation," he said.

"They are clearly the subject of oversight by the New South Wales Ombudsman and the Police Integrity Commission should they see fit to do so," he said.

"Given our recent experience, I would subject that the NSW Ombudsman will be paying close attention to both investigations."

The Assistant Commissioner says the police officers involved in the incidents were from Fairfield and Parramatta - outside of the local area command.

He told a press conference an officer was wrong to order members of the public to stop filming and will be spoken to.

"It is contrary to our media policy," he said.

"I would suggest that unfortunately, it shows a degree of naivety of the police involved who made those comments.

"We understand and accept, and in fact support the right of the community to film anyone in a public space. We do it ourselves as part of our operational duties."

Assistant Commissioner Murdoch says he does not believe the incident will permanently damage relationships with the community.

"Our relationship locally with the gay and lesbian community is first-class," he said.

"Policing in the western suburbs is a different kettle of fish, and we need to take account of that."

The Police Minister Michael Gallagher says CCTV in the area will help in the investigations of the alleged assaults.

He says the type of footage which has been released is confronting.

"Any piece of footage that sees police officers and a person in conflict is always going to be viewed as disturbing," he said.

"I'm not aware of the circumstances leading up to the event. I think what needs to happen is the entire event needs to be looked at in its totality."

This morning New South Wales Police released a statement saying they had charged the man with assaulting police, resisting arrest and using offensive language.

He has been ordered to face court in April.

A second man has been charged with assaulting police.

Sorry, this video has expired NSW Police to investigate alleged Mardi Gras brutality ( ABC News )

Sydney state independent MP Alex Greenwich says he has heard several claims of police heavy-handedness at the Mardi Gras.

"I am aware and my office has been contacted by others who have experienced similar interactions with police during Mardi Gras," he said.

"Hopefully those matters will also be investigated."

He said he would bring the matter to the Police Minister's attention as a matter of urgency, and would be calling for a full investigation.

Mardi Gras co-chairman Peter Urmson told ABC News Breakfast that "the gay and lesbian community is really quite up in arms about this issue."

"Looking at the footage, the guy that's being apprehended doesn't seem to be too aggressive and we just wonder how this could come to be. It just seems as though the guy is being basically picked on," he said, adding that organisers knew the man's identity but were not releasing it for privacy reasons.

"We know of a second incident that allegedly is similar and we've received medical records from the person that felt that they had been aggrieved," he said.

"[Mardi Gras] was born out of police brutality 35 years ago [and] I think now we kind of wonder how far have we really come.

"We have extensive working relationship with the New South Wales Police and there's lots of meetings that happen beforehand and there's lots of debriefs - and obviously this will feature heavily in the debrief over the next few days."

Scott Weber from the New South Wales Police Association says people should not rush to judgment.

"The Police Association hasn't seen the footage from the Mardi Gras yet, but in saying that, we need to go down the proper lines of investigation," he said.

"We've seen time and time again where footage looks very adverse, such as we saw at the Sydney Cricket Ground, but then on proper investigation it was easy to highlight that the police officer's actions were justified."