A Toronto police officer has been rushed to a trauma centre with life-threatening injuries following a vehicle collision in the city's west-end on Saturday afternoon.

The collision happened just after 4 p.m. near Bloor Street West and Neilson Drive.  Photos from the scene show a smashed up unmarked police car near a tree with a damaged trunk. 

Deputy police Chief Peter Sloly said Const. John Zivcic had undergone surgery and is in serious condition.

"The officer has undergone a series of medical operations. The most recent one we were advised by the surgeon that the officer has received life-threatening injuries," Sloly said, calling the seven-year veteran of the force a "strong performer" and an "up-and-coming police officer."

One witness said she heard a loud crash and came out of her house to see the officer lying face down on the sidewalk with a lot of blood.

A police motorcade of nearly a dozen vehicles cleared traffic for the ambulance as it rushed towards St. Michael's Hospital downtown.

Toronto Police Association president Mike McCormack said the officer would remain in the intensive care unit and "we're just going to monitor the situation as it unfolds."

Neither McCormack or Sloly would comment on the exact nature of the officer's injuries.

"We're just going to focus on providing the support we can to John and his family," Sloly said.

It's not clear whether the officer was in pursuit of another vehicle when the collision occurred.

Another vehicle at the scene appeared to also be involved in the collision.

Sloly said the Special Investigations Unit had not been called in because the driver of the other vehicle only suffered minor injuries.

A police reconstruction team taped off a large area around the intersection while they investigate.