A Chinese international student drowned after being swept off rocks in southeast Sydney at the weekend while posing for a photograph, Australian authorities have said.

Onlookers had jumped into the water immediately to try to help the woman, but she could not be found, Fairfax media reported on Monday.

Authorities and rescuers performed a search for the 24-year-old Chinese student at Bare Island, La Perouse, locating her body just after 3.30 pm on Sunday.

A New South Wales Police spokeswoman said the woman was believed to have been studying in Sydney.

"Police have been told she was posing for a photo at the time, and she was swept off the rocks by a large wave," the spokeswoman said.

It was not clear whether the victim could swim.

One witness who wrote on social media said the woman and her companions "were trying to get the 'best' pic... They looked shattered."

La Perouse is popular for weekend picnics.