Police say they knew for weeks of plans by two youth gangs to cause havoc at Melbourne’s White Night event.
Assistant Commissioner Stephen Leane told reporters on Sunday officers had intelligence the groups would meet in the city and cause trouble well before the night.
In turn, police had formulated a “well planned” response to any threat of violence.
“A lot of (social media) sites aren’t locked so police have become adept at (monitoring them),” Mr Leane said.
Officers used pepper spray to break up a rowdy confrontation between two youth groups at Federation Square about 1am on Sunday.
Mr Leane said those involved were aged between 14 and 19 and had been discussing the face-off for weeks including via social media.
“As far as we can see it’s the United Nations of groups. They merge but they take a dislike to each other and for some reason the groups were deciding last night they’d have a go.”
Hundreds of police swarmed the area, including members of the mounted branch and public response order unit, standing between the opposing groups who “looked like they were going to flare up,” according to Mr Leane.
Asked if he thought the trouble was linked to the Apex gang which disrupted last year’s Moomba parade, he said, “I’m not sure if Apex even still exists”.
Instead, he described the potential participants as “networked” offenders.
More than 20 arrests were made over the course of the night, including at Footscray train station where police found youths in possession of a can of OC spray.
Other weapons including knives and knuckle dusters were also seized.
About 500, 000 people attended the annual White Night event and authorities say they were pleased overall with behaviour on the night.