Waterloo Regional Police say Victoria Street South is closed between Paulander Drive and Lawrence Avenue after a two-year-old boy was struck by a vehicle.
They say he has been transported to an out-of-region hospital with life-threatening injuries.
They are asking people to avoid the area.
The daily email you need for
Kitchener's top news stories.
Police made the announcement on Twitter at around 9 a.m.
They have not released further details about the incident.
More to follow.