A house party involving young teenagers in the Christchurch suburb of Phillipstown, which got out of hand, led to the arrest of several people on Friday night.
Police went to the Percy Street house about 9pm on Friday after calls from neighbours that the party was out of control.
They returned about 10.30pm and a police spoksperson says there were reports of about 100 people on the footpath, some of them intoxicated and throwing bottles.
Those at the house had been charging a $2 entrance fee and Acting Inspector Paul Reeves says numbers grew to about 300, many in their early teens, as news of the party spread through social media.
He says several people were arrested for disorder and willful damage after fences and letterboxes were damaged and property was tagged.
Mr Reeves says efforts by officers to break up the party were hampered by small groups which hung around the area.
"With groups of 300 it's hard to disperse them without pockets breaking off."
He says it took officers about two hours to break up small groups of revellers and move them on.
Mr Reeves says people need to realise that when police turn up in such situations they should disperse and leave the area to avoid any ongoing trouble.
"With social media these incidences spiral out of control and before you know it there's major problems," he says.
It's not clear exactly how many people were arrested or when they will appear in court.
