The footage, which was said to have been recorded at the Stereosonic festival, held last weekend in Sydney, was posted on Facebook on Thursday morning and had been viewed more than 250,000 times within hours.

The shaky footage, which appears to have been shot on a mobile phone, shows a group of men wrestling with each other and throwing punches seemingly indiscriminately.

One man, wearing blue shorts, can be seen in the early stages of the footage putting up his fists, before a person in a white T-shirt approaches him from behind and punches him on the right side of his head.

The man immediately falls to the ground and appears to be unconscious. The face of his attacker is not shown in the footage.

Security guards and onlookers rush to the fallen man's aid, and turn him on his side.

However, at least one more scuffle breaks out around them as they try to administer first aid.

Two females are shown struggling to get through the crowd, with one yelling: "I'm trying to get her out!"

The performer on stage can be heard at one point saying: "Thank you Sydney, we love you."

The two-day Stereosonic music festival was held at Sydney Olympic Park last weekend.

Stereosonic has been contacted for comment.

By Thursday afternoon, the footage had been shared more than 1000 times on Facebook, where people were criticising the behaviour of those involved in the brawl.

"this is what happens when you get a bunch of full high level testosterone drunkin half wits together in the same place [sic]," wrote one person.

Another said: "WAYYYYYYYYYYYYY too much testosterone and weight gain powder right there."

Police said that the incident had not been formally reported to them.

However, despite this, "the violent nature of the incident is of major concern to NSW Police.

"It reflects on the disappointing behaviour of some of those who attended the event."

Police said in a statement that a high-visibility police operation was in place at the Stereosonic festival, including the Dog Unit, the Riot Squad and the Mounted Unit.

More than 81,000 revellers attended the festival and police searched more than 830 over the two days.

One hundred and ninety-six people were found in possession of prohibited drugs, including MDMA (ecstasy), cocaine, cannabis, GHB and ketamine.

Thirteen were charged with supply of a prohibited drug and 169 with possessing a prohibited drug.

Fourteen people received cannabis cautions.

Officers patrolling public transport to and from the event charged a further 38 people with possessing a prohibited drug and one with supplying a prohibited drug.

Thirteen people required medical treatment and were taken to hospital, most with drug-related ailments.

Assistant Commissioner Frank Mennilli said one man, aged 21, was lucky to be alive after he was found not breathing.

The man was given CPR and taken to Concord Hospital in a serious but stable condition. He has since been released.

"We do not apologise for targeting illegal drugs, because they pose a very real health risk and can prove lethal, Mr Mennilli  said.

"These operations are not about us being the fun police.

"They're about us making sure revellers can have a good time in a safe, secure and drug-free environment."

Anyone with information about the brawl should contact Crime Stoppers on 1800 333 000.