A woman was allegedly assaulted as she sunbathed topless at Point Chevalier Beach in Auckland.

A woman sunbathing topless on a beach says she was left terrified after she was allegedly assaulted by a group of people who kicked sand at her.

The incident happened at around 5.15pm on Thursday as the woman was sunbathing alone at Point Chevalier Beach in Auckland.

She told Stuff she would go swimming in the sea before 10 minutes of sunbathing twice a day over summer, however Point Chevalier was not her local beach.

She had been sunbathing shirtless for about seven minutes before she was approached by a group of about 20 people at the northern end of the beach near the steps to Coyle Park.

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The woman heard people saying "excuse me", but had not realised it was directed at her. Suddenly, a towel was thrown across her chest and two women started throwing "copious" amounts of sand over her, she said.

One of the alleged attackers was said to have shouted and swore at the sunbather, with aggression in her voice, while the other recorded the incident on a mobile phone.

The women told her there were children nearby, to which she responded it was not illegal to sunbathe shirtless.

"I feel as a New Zealand woman it is my right to bare some of my flesh," she said, adding that it was good for her mental, spiritual and physical well-being.

She added that she had a small chest anyway, and was more concerned about her "belly fat" being exposed. Even then, they should have just diverted their eyes, she said.

"I was perfectly minding my own business."

The woman did not plan on returning to Point Chevalier beach for a while, as she was left "terrified" by the attack. She was afraid the women would post photographs of her online if she reported them to police.

Keen to get away from the scene, she skipped the changing rooms and got changed in her car, still covered in sand.

"I didn't want to be there any longer than nesseccery."

Reflecting upon the incident, she felt disappointed a group of about four adults sitting 15-20 metres away didn't step in to help, especially given how "brutal" the women were being.

"Nobody actually came to intervene."

She phoned 111 in the car once she had driven away from the beach, where it was agreed she should go to a police station to make a more formal complaint.

A police spokesman confirmed officers had received a report from a witness to an incident at Point Chevalier Beach where a woman on the beach had sand kicked at her.

When the incident was reported, the witness had left the area and was advised to report to the nearest police station.

Sunbathing topless is not against the law, but anyone indecent exposure - anyone who intentionally and obscenely exposes their genitals in public - is a summary offence, punishable by up to three months in prison, or a fine of up to $2000.