At a 1 a.m. news conference, a clearly upset Police Chief Bill Blair said the Monday night incident was "unprecedented" in Toronto history and there were two gunmen.
More composed Tuesday morning, Blair told reporters there was concern the "potential for retaliatory violence is high."
A 14-year-old female and 23-year-old male were pronounced dead at the scene.
One of the shooting victims was a 22-month-old child, Blair said.
No one in the neighborhood would speak to various television news outlets, saying they feared for their safety.
The police chief said witness silence was hampering the investigation and said the shooting spree of "deprived indifference" demanded a "response from the entire city."
At a midday news conference from the crime scene, Mayor Rob Ford was clearly upset. Toronto has seen several public deadly shooting sprees in recent weeks, but Ford haltingly said the city is still the "safest in the world."