Police said the Tuesday morning crash involved a flatbed truck and a car and occurred shortly after 9 a.m.
An Ornge air ambulance was dispatched and has transported one person with critical injuries to the trauma centre at Toronto's Sunnybrook hospital.
Another person was killed in the crash, police said.
The highway was closed in both directions to allow the helicopter to land, but the westbound lanes have since reopened. All eastbound lanes at Trafalgar Road will remain closed for several hours, police said.
Eastbound traffic is being directed off the highway at Trafalgar Road and the eastbound ramps to Highway 407 are also closed in the area.