A St Heliers resident called the police after witnessing a group of around 10 people engaged in sexual activity in public at a central Auckland nudist beach. 

Police say they received a report of a sexual incident in Ladies Bay, St Heliers, just after 6pm on Friday. 

The resident and his fiancee went to Ladies Bay near their home for a swim after work around 5pm. 

As he was collecting his towel after his swim, the man said he heard noises and saw a group of people having sex on the grass bank at the beach. 

"It was so outrageous. So bizarre," said the man, who spoke to the Herald on the condition of anonymity. 

The couple then ran up the hill and called the police. They said an officer turned up within five minutes and proceeded to try to locate the group. 

The man said what he saw made him feel "revolting". He said there had been children around "just minutes" beforehand. 

It "shook us up", the man says, who was supposed to be going to a party with his fiancee tonight but they opted to stay in after the experience. 

He said there were around 10 people in the group, made of up of men and women, who were involved in the sexual activity. 

There were also two men that appeared to be standing guard and one of the men locked eyes with him when he looked at him. 

"An officer attended, made himself known and spoke to those involved, and the matter has been dealt with," a police spokesman said 

Historically, Ladies Bay was a nude swimming area for women, with neighbouring Gentleman's Bay popular with naturist men. 

But most of the naked visitors to Ladies Bay now were male.