A teen's 18th birthday party spilled into chaos after more than 150 uninvited guests showed up, creating an uncontrolled mess in New Plymouth on Saturday.

Officers were called to Fitzroy Rd at 10.45pm on Saturday after bottles were being smashed, according to Police.

The majority of those in attendance were aged between 15 and 19.

Sergeant Ross Wright told Fairfax it is a great concern when parents aren't aware their children are attending parties and drinking alcohol.

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"With most of these kids on social media, they come from the hills to attend...

"Many of their parents would have no idea that their child was heading to a party and or drinking alcohol, or where the alcohol supplied came from."

According to Wright, four patrol cars showed up to the scene and were there for an hour before restoring peace just before midnight.

He warns hosts to research their obligations and recommends having enough adult supervision to prevent any unwanted guests creating trouble.