Neighbours rushed to a unit on Ninth Avenue in Campsie after they heard a woman screaming for help at 8.45pm yesterday.
They discovered a woman with a stab wound to the thigh.
“I opened the door and she was crying, just bleeding a lot, and a guy with me called the police,” one neighbour told 9News.
When police arrived, they found a second person, a 46-year-old man with multiple stab wounds to his face, arms and chest.
He was taken to Royal Prince Alfred Hospital in a critical condition.
The 53-year-old woman was treated at the scene and is recovering at St George Hospital.
A 25-year-old man was arrested outside of a nearby home and was taken to Concord Hospital.
He remains there under police guard.
9News understands the two victims are a couple.
Residents of the apartment building say the younger man may be related to them.
Ninth and First Avenue remain closed as police conduct line searches between the roads.
Students of the nearby Harcourt Public School have been directed through the back gate as the main front entrance is closed.
Investigations are ongoing.
