A party in a Rotorua suburb got out of control when 200 uninvited teenagers show up because of phone texting.
Rotorua police area commander Inspector Bruce Horne said the organisers of the party on Saturday had gone to some effort to prevent trouble but unwanted teenagers turned up and caused chaos.
He said it proved parents should "exercise caution'' when thinking about holding such events for young people.
Other residents complained about the party, which resulted in youths fighting and causing trouble in their street.
Mr Horne said the organisers had intended it to be alcohol-free and limited the number of people invited. The party had adult supervision and private security.
"However, what they were not able to control was information about the party spreading quickly by text message, resulting in about 200 uninvited and unwelcome teenagers arriving with alcohol,'' he said.
"Many had clearly already consumed large quantities of alcohol before they arrived at the property.''
Mr Horne said it wasn't long before fighting broke out and bottles were thrown, which resulted in police being called.
About 16 police officers attended and 12 people were arrested.
"Unfortunately, this sort of event is an all-too-common occurrence and is one that our police staff are faced with on a regular basis and it highlights the problem of alcohol abuse in our community,'' he said.
"We would urge parents and caregivers to take an active interest in their children's lives, know where they are, who they are with and what time they will be home.
"In this case, in spite of the organisers' best efforts, it still went horribly wrong.''
He said there was now research which showed there were many risks associated with teenage drinking, and a number of reports had highlighted the need for a change in attitude toward the use of alcohol in New Zealand communities.
"Binge drinking is not okay, it's dangerous,'' he said. "Likewise, it is not okay to provide young people with alcohol if they are under the legal drinking age of 18, in fact it is illegal.''
Mr Horne said New Zealand research showed alcohol was a factor in one-third of all reported crime and one of the concerns about young people drinking was they were more likely to become a victim or perpetrator of crime.