A woman and her friends have described their horror after a man allegedly sprang out in front of them from behind bushes, "violently masturbating" at them.

The incident happened as a new mum and her friend were walking to their car at Wattamolla Beach in the Royal National Park, south of Sydney.

Speaking to 7News, the woman, who wished to remain anonymous, said:

"He was violently masturbating at us. We yelled at him and tried to take a video to pass along to the police. He wasn't fazed at all and continued going at it while staring at us and following us on the track."

The man is believed to be between 30 and 40 years old and was wearing a khaki hat with a black flap, khaki shirt, and khaki boots. He was also believed to be wearing a camera on his neck.

Meanwhile, another report has emerged of a second incident (involving a different person) around the Cronulla Shire several hours later. A man exposed himself to another woman before running away.

The woman posted about the incident on Facebook, saying she was sickened to think the man had been watching her for over an hour.

She wrote:

"Be careful, ladies, and think twice before swimming there alone or at night! And trust your intuition if you see something weird."

The man is described as a Caucasian male, about 20 years old, tall and skinny with dark short hair, and was wearing a black t-shirt and blue and white shorts.

She now warns other women, visiting the Salmon Haul Reserve alone or at night, to "trust your intuition if something feels weird."

She also urged her followers to "think twice before swimming alone."

In a Facebook post, Sutherland Shire Police and Command wrote:

"Sutherland Shire Detectives are investigating two separate acts of indecency reports which have occurred at Cronulla and Wattamolla…"

"The first incident occurred at Wattamolla Beach at about 5.15 pm. The male has exposed himself and performed indecency towards a female. He is described as a Caucasian male, about 30-40 years old, wearing a Khaki hat with a black flap, khaki shirt, and khaki boots."

"The second incident occurred at Salmon Haul Reserve (Cronulla) between 7 pm and 8 pm. A male had exposed himself and performed an act of indecency towards a female and then ran away when she spoke to other people. He is described as a Caucasian male, about 20 years old, tall and skinny, with dark short hair, wearing a black t-shirt and blue and white shorts."

According to Charity Victim Support, sexual harassment is defined as 'any unwanted behavior of a sexual nature that makes you feel humiliated or intimidated, or that creates a hostile environment.'