A large group of youths gate-crashed a popular Caroline Springs festival at the weekend, leaving a teenager in hospital and some festival-goers robbed of their mobile phones and handbags.

Melton council’s annual Summersault festival turned sour about 10pm on Saturday when a group of an estimated 30 to 40 teenagers descended upon a crowd watching the festival finale’s fireworks display.

Six people reported having their mobile phones snatched from their hands as they were filming the fireworks, and two people have reported being assaulted, according to a Victoria Police spokeswoman. Debbie Tesoriero’s 16-year-old son Jack spent the night in hospital after he was punched and had his phone stolen at the event.

“My understanding is that he was knocked out. He didn’t know where he was, he didn’t know what day it was,” Ms Tesoriero told the Seven Network.

It’s believed Jack had been walking a friend back to a car when he was jumped by the group, she said.

One witness, Joe Cuic, said a “big pack” ran through the crowd, grabbing mobile phones and handbags as festival-goers recorded the fireworks. He then saw youths throwing rocks at apartment buildings.

“Out of nowhere, everyone’s gone from standing there watching, having a lovely time, to people just running in all directions,” Mr Cuic told the Seven Network.

Melton councillor Steve Abboushi, who attended the festival with his family, said he left halfway through the fireworks display when he could sense trouble was brewing.

“I was there with my four-year-old and I could sense there was something brewing so I packed up, jumped in the car and called the police,” he said.

Cr Abboushi said the council had ample security measures in place, but there was little it could do to stop being “gate-crashed”.

“How do you stop people jumping on public transport and gate-crashing a party,” he said. “There was adequate security and a police presence; we were just outnumbered.

“My personal view is that we need to review the youth justice system and offer more support for disenfranchised youths living on the fringe,” he told Star Weekly.

The alcohol-free festival, promoted as a family-centric event, is held annually and features music, food stalls and rides.

A council spokeswoman said the festival was attended by tens of thousands of people.

Anyone with information about the incident is asked to contact Crime Stoppers on 1800 333 000 or www.crimestoppersvic.com.au