The province's police watchdog is investigating after officers shot a knife-wielding man at the scene of a homicide in Peterborough, Ont., on Friday night.

Peterborough Police Service officers responded to a call about an assault at a Middlefield Road home around 11:45 p.m., according to the Special Investigations Unit (SIU).

Officers arrived on scene to find a 52-year-old woman's body and a young man wielding a knife, SIU said. 

Police opened fire and the 25-year-old man was rushed to Peterborough Regional Health Centre, and then transported by ambulance to St. Michael's Hospital in Toronto, where he underwent emergency surgery.

He is now in the intensive care unit.

Peterborough homicide detectives are investigating the woman's death. 

The SIU investigates any time there is death, serious injury or allegation of sexual assault involving police.