Peel Regional Police say a female driver in her 70s was taken to a trauma centre following a two-vehicle crash in Mississauga on Thursday morning.
Police said the crash happened just after 7 a.m. near Danton Promenade and Derry Road, just west of Winston Churchill Boulevard.
Paramedics said there were three patients in total.
Two were assessed at the scene and their injuries appear to be minor, paramedics said. Police said the everyone but a driver was out of their vehicles.
A woman was initially transported in serious but non life-threatening condition to a trauma centre, paramedics said. In a later update, police said her injuries are considered life-threatening.
Officers initially said the woman was in her 70s, but now say she is, in fact, 69-years-old.
Police temporarily closed the area as its major collision bureau has taken over the investigation.
In an update just before 5 p.m., officers said the road has reopened.