Authorities said another person was injured in Mississauga. The suspect fled to Milton and thought he shot three other people, killing one, police said.
Officer Andrew Hong, 48, of the Toronto Police Traffic Unit was shot at close range and died on the spot, chief James Ramer told reporters.
“This is devastating news for his family and all members of the Toronto Police Service and our entire police community,” the chief said. “We will rely on each other as we work to support Agent Hong’s family, and each other, in our grief.”
Hong leaves behind his wife and two children. He had been in the department for 22 years.
Peel Regional Police in Mississauga previously said they were called to the scene of a shooting at the intersection of Argentia Road and Winston Churchill Boulevard, where two people were killed shortly after 2 p.m. ET.
The victim who was taken to hospital has “life-changing injuries” and is in a trauma center, Peel Regional Police Chief Nishan Duraiappah said during the briefing. He called the agent shooting an ambush.
After the suspect fled, three people were shot dead on Bronte Street South in nearby Milton, Halton Regional Police said. One person was pronounced dead on the spot and two others were taken to hospital, according to police. Their terms were not immediately available.
“We believe this was the same suspect involved in the shooting here in Mississauga,” Duraiappah said.
Both police agencies said they are investigating the link between the two incidents and believe they are linked to the same person.
Canadian Prime Minister Justin Trudeau tweeted about the Ontario shooting on Monday.
Milton, Mississauga and Hamilton are not far west of Toronto.
Rob Frehse and Isa Kaufman Geballe of CNN contributed to this report.