Police were called to the Jane Street and Driftwood Avenue area in the city's northwest after gunshots were heard, a Toronto police release says.
The officers discovered five people with apparent gunshot injuries.
Paramedics say one has life-threatening injuries, two suffered "very serious" wounds and the remaining two have minor injuries.
The release says that during the arrests, one of those arrested was shot "in an interaction with police." That person has non-life-threatening injuries.
Ontario's Special Investigation Unit (SIU) has been called in, which prevents Toronto police from commenting further.
The SIU says a male was shot by police on Elmhurst Drive in Toronto near Islington Avenue and Rexdale Boulevard as Toronto police were investigating a vehicle.
Elmhurst Drive is about eight kilometres west of Driftwood Avenue.
The SIU probes all incidents involving police in Ontario that result in serious injury or death.