Two women in their 20s and a 40-year-old man have died and another woman is fighting for her life after being pulled from the water unconscious at Victoria's Phillip Island.
Emergency services responded to reports of four people struggling in the water near Newhaven about 3.30pm on Wednesday.
Three women and a man were pulled from the water unresponsive, police said.
First responders administered CPR on all four but three died at the scene.
A woman in her 20s was airlifted to The Alfred Hospital in a critical condition, according to Ambulance Victoria.
The four were swimming at an unpatrolled location near Forrest Caves, a Lifesaving Victoria spokeswoman said.
The family and friends of the victims were very upset once they arrived on the scene, a witness told 7News.
"There seemed to be a group of about 10 people who would have come here for just a really nice day and obviously it's ended in tragedy," Alex Tzatzimakis told 7News.
"(They were) crying and comforting each other."
The Visit Phillip Island tourism body said the caves are formed by erosion of the cliffs and are only accessible at low tides.
Police will prepare a report for the coroner and are not treating the deaths as suspicious.
