The Special Investigations Unit (SIU) has invoked its mandate following an incident in Burlington.
Halton Regional Police Service said its officers responded to a call in the area of Cornerstone Drive.
No other details were provided.
Police said there is no risk to public safety. The SIU has taken over the case.
The SIU is an independent civilian agency that probes incidents where people died or were seriously injured. Investigators also review incidents where sexual assault has been alleged, or a firearm was discharged at a person.
