Three people found unconscious on boat circling Melbourne's Port Philip Bay

Three people have been found unconscious on an out of control boat near Melbourne.

Police believe a carbon monoxide leak is responsible.

The boat was circling 500 metres offshore in Port Phillip Bay and two men and a woman were found unconscious on the deck on Tuesday night, police said on Wednesday.

A 60-year-old man was airlifted to The Alfred Hospital and the two others were taken to Geelong Hospital.

All are were in a stable condition on Wednesday, the hospitals said.