A young woman who was filmed being shoved to the ground by an officer during the Moomba festival was interfering with an arrest, police said on Monday.

Shocking mobile phone footage captured the moment a woman was pushed by a Protective Services Officer at Flinders Street Station in Melbourne's CBD at 1.30am on Sunday.

The officer said 'step back, step back,' before he pushed her with such force that she fell on her back and slammed her head on the wall.

In a press conference on Monday, police said the woman had been previously 'dealt with' by officers and was impeding an arrest.

The officer (pictured) said 'step back, step back,' before he pushed the woman (in the yellow top) with such force that she fell on her back and slammed her head on the wall

The woman was pushed by a Protective Services Officer Flinders Street Station in Melbourne's CBD on Saturday night

'She decided to walk in on an arrest scenario and from there one of our PSO's has taken some action to protect his colleagues but also the zone in which they're operating in,' said Commander Tim Hansen.

'They're an uncertain environment and they're a dangerous environment,' he said of arrest zones.

'If we give you advice to keep out of an area, it's with good reason and good intent.

'We were giving her some advice [that it was] probably time to head home'.

Commander Hansen admitted the footage was confronting and said it was under internal review.

The moment was filmed by a 15-year-old reveller who said officers had blocked off a platform because of a fight when the woman went up and tried to negotiate with them.

Saturday night: Several police officers were needed to arrest a violent youth in Melbourne's CBD on Saturday night

Brawling groups of ethnic youths have marred the Moomba Festival yet again, with five people arrested following three separate incidents in Melbourne's CBD

'She tried to get past them because she kept saying she was in a rush to catch her train, it was real late,' he said.

'When she walked up to the cops he told her "back off", she just said "I'm going this way".'

'She kept trying to get past him, that's when he threw her towards a wall.

'Her face was all bruised and beaten, she had a bruise on the right of her lip straight away.'

His mother said the incident left her doubting whether her children could have faith in the authorities.

'My son's 15 and my daughter's nearly 12, if they can't trust police then what?' she said.

'If that was my daughter, oh my god.'

On Sunday, the Professional Standards Command said it had received a third-party complaint which will be investigated.

Confronting footage taken outside St Paul's Cathedral showed dozens of young men and women watch as a topless man threw punches (pictured)

Dramatic footage posted online (pictured) showed more than a dozen teenagers sprinting down a set of escalators at Flinders Street station

Protective Service Officers are employees of the AFP. They guard buildings and assist police at events such as festivals.

Over the weekend, Victoria Police arrested 20 people for assault, drunken behaviour, drugs and weapons offences as Moomba festival was spoiled by violence.

Three brawls between warring gangs of youths at Federation Square and Flinders Street Station between 10pm on Saturday night and 2am the next day resulted in two of the arrests.

Commander Tim Hansen described the incident as a 'rolling brawl' and while it occurred during the Moomba weekend it wasn't directly linked to the festival, as clashes involving groups from Melbourne's southeast and western suburbs attracted police attention most weekends.

'They are networked on social media, some of them assume banners and tags of street gangs and there are existing tensions between them,' Mr Hansen added.

'We've been very successful in disrupting planned fights in the past, but on Saturday night there was nothing significant [in the intelligence] that indicated we would see a fight.'

During the weekend, police proactively removed certain youths from the Moomba precinct and took others off the street before the weekend kicked off.

Of the 20 people arrested between Friday and Monday morning, 10 were arrested in the Moomba Precinct for drugs, weapons and assault offences.

The numbers indicate a fall in crimes against the person and criminal offences during the three-day festival, Mr Hansen said, although he didn't give comparable figures.

'Our extra police presence across the CBD assisted us greatly, and helped incidents be dealt with very quickly.'

