Ontario Provincial Police Sgt. Kerry Schmidt said it happened at around 5 p.m. at Simcoe Street, between the off and on-ramps.
Schmidt said one person was taken to hospital with life-threatening injuries and Highway 407 was blocked in the area as a result of the crash.
“Reconstruction teams and Toronto OPP are on scene,” Schmidt said. “If you happen to be a witness, or have information, please call the Toronto OPP.”
Schmidt said he did not have a timeline for reopening.
There is no word on what may have led to the crash.
A spokesperson for Ornge air ambulance told Global News they were called to area for a single-vehicle rollover shortly after 5 p.m., but that call was later cancelled.