"It's a number of street gangs that are in conflict with each other," he said.

"There's territorial disputes ... and also we're actively monitoring the interaction of these groups."

Mr Hansen said police were investigating other incidents that were "related to a broader group of people that are networked and connected".

It was hoped the raids had "dismanted and disrupted" those networks.

Mr Hansen said the arrests were made in relation to alleged fights that had occurred in the past month across Melbourne's western and south-eastern suburbs.

Gang members were not of any particular ethnicity and police were monitoring people of all backgrounds.

"Over the course of White Night, we're being supported by community leaders from the African community, from the Maori community and from the broader community. We will have a number of community leaders out with us on patrol Thursday, Friday and Saturday night," he said.

The riot at Moomba in 2016 involved scores of youths believed to be members of gangs then known as Apex and Islander 23. It is not known if members of the same gangs are involved in the current escalating tension.

"These gangs have been with us for some time," Mr Hansen said.

"They are fluid in size - they change - people come in and out of those gangs, so they morph quite a bit. They change names from time to time. There is a level of connection that occurs across social media predominantly.

"Some of these relationships are born out of when kids are in custody."

Mr Hansen said there would be more than 500 officers on the ground in Melbourne's CBD from Thursday night, in what he described as one of Victoria Police's most "resource heavy" events.

He warned people planning on causing trouble police would be waiting.

"We aren't scared of them, we aren't afraid of them and if those people want to come into the city on the weekend and cause problems then ... we'll be here waiting for you," he said.

Mr Hanson said there was a "very small element" that had shown a propensity to disrupt major events.

"We're hopeful that the main players who we believe are going to cause a risk to community safety won't be in a position to do that, through White Night," he said.

Police and event organisers have been developing a plan to thwart a potential riot or hostile vehicle attack since the beginning of the year, according to White Night director David Atkins.

Mr Atkins – who commended police for the arrests – said a “massive” number of police officers and more than 200 event security staff will be watching for any disruptive behaviour.

“This has been front of mind for us … police have been very, very active – they are deploying hundreds of officers across the three nights,” said Mr Atkins.

“We're very confident in the support of [police] and all emergency service stakeholders to be able to respond [to a threat] ... in a very effective way.”

Mr Hansen said police preparations for this weekend had been “significant”.

As well as White Night, several prime time sporting events are also taking place, including two blockbuster AFL games at the MCG and the Boomers-USA basketball match at Marvel Stadium.

Under the Control of Weapons Act, police will have increased search powers in the CBD and festival area, which grants police additional powers in designated areas.

The powers will include “increased powers to stop, search and ask for names and addresses,” Mr Hansen said.

Melbourne's White Night festival will be held over three nights, from Thursday to Saturday.