Emergency crews were called to Dearbourne Boulevard and Dorchester Drive, in the Steeles Avenue and Torbram Road area, just before 7 a.m. for reports of a pedestrian-involved collision.
Police said a woman was taken to hospital via paramedics in serious condition.
The driver did not remain at the scene of the collision, police said.
The area was closed for the investigation.
There is no word on the type of vehicle involved.