At least three serious assaults, involving young people being knocked unconscious, were reported amidst large disorder in Dinosaur Park, police said.
Numerous other more minor assaults were also reported.
Police were called to the park at about midnight to find the large gathering and multiple fights breaking out.
Acting District Commander Inspector Matt Scoles said it was disappointing that many of those present appeared to have been supplied alcohol.
"We know it’s a time of year where lots of people are out celebrating and having a good time," he said
"But we need parents to make sure their young people are acting responsibly, knowing where they are and what they are doing.
"I’m sure many parents would have been horrified to learn their teens had been putting themselves in danger, consuming excessive amounts of alcohol and engaging in violent altercations.
"It’s extremely dangerous for all involved when we have young people drinking under the legal age and gathering en masse without any supervision."
Inspector Scoles said many of those involved were from out of town, with families in Wānaka on holiday.
He urged families on holiday to stick together and enjoy time away from home responsibly.
"Please, keep track of your kids, and have a plan with them around how everyone is going to stay safe.
"We don’t want to be knocking on your door at 2am telling you something serious has happened involving your teenager."
