Beach walker Betty Knight was horrified by the mess left behind by the partying youths.
"It is disgusting, the worst I have ever seen. Bottles, cans and rubbish were strewn everywhere," she said.
The mess, including broken bottles, littered a large area of beach and dunes halfway between Sunrise Ave and Sandhurst Drive. "It is positively dangerous."
Partygoers also lit two fires, one on the beach and another in the dunes.
She said it looked like there had been a huge party.
"We were horrified."
Council contractors responded to calls and, helped by an unidentified youth, cleaned up the area yesterday morning.
Senior Sergeant in charge of the Mount Police Station, Deidre Lack, said a call was received about teenagers partying on the beach at Omanu but they had gone by the time a patrol arrived.
Council parks and recreation manager Mark Smith said a call about broken bottles on the beach was received from a resident at 9am yesterday and contractors were told to clean up the rubbish as a matter of urgency. "It's disappointing to see our beaches left in this condition. We really appreciate our residents letting us know when something like this happens, so that we can get something done about it quickly and avoid any injuries," he said.
The Mount Fire Service was called to minor fires in the vicinity of Maranui St at 8.51pm and 11.28pm on Tuesday night.