The collision happened just after 4 p.m. near Bloor Street West and Neilson Drive. Photos from the scene show a smashed up undercover police car near a tree with a damaged trunk.
A police escort of nearly a dozen vehicles cleared traffic for the ambulance as it rushed towards St. Michael's hospital downtown.
It's not clear whether the officer was in pursuit of another vehicle when the collision occurred.
The CBC's Steven Bull said another vehicle at the scene appeared to also be involved in the collision.