Five teenagers have been arrested in Nelson after an underage party got out of hand in Victory Square on Wednesday night.
The police say they got calls from concerned residents at about 10pm after drunk youths spilled out of the party onto Vanguard Street in the city.
A security guard and members of the public were allegedly assaulted.
Sergant Shane Miles said no one was seriously injured in the assaults, but three people were treated by paramedics at the scene.
But he said someone could have been badly hurt and it is a perfect example of why unsupervised youth parties involving alcohol are a bad idea.
The five youths arrested spent the night in police custody and will face disorder and assault- related charges in the Nelson District Court.