Victims, possibly including children, were reported to be spread over several blocks and a number sustained significant injuries, paramedics reported.
Paramedics have reportedly been told the gunman is no longer active.
Police and other emergency services are responding to multiple shootings in the area of Danforth Avenue in Toronto, officials and witnesses say.
Camera IconA tactical officer works the scene of
Some victims are being treated at the scene, while others have been taken to local hospitals.
One of the victims is believed to be a child, according to local news outlets but the victims' conditions are unknown.
Police escort civilians away from the scene of the shooting.
The Toronto Transit Commission said trains are not stopping at Chester as a result of police activity.
Tiger, Spieth set Open alight
Afternoon all and welcome to coverage of the final round at Carnoustie where Jordan Spieth is one of three tied for the Open lead. It caps a stunning stretch for the 15th-ranked Molinari, who has won on the PGA and European Tours in the previous two months.