Six people were injured in a pileup that occurred shortly after noon Wednesday on Highway 30 in Chateauguay, Monteregie.
According to the Surete du Quebec (SQ), collisions occurred westbound following a slowdown in traffic.
The driver of a tractor-trailer would have rammed the rear of the vehicle in front and there was subsequently impacts with other vehicles.
Among the injured, the two have been seriously and feared for the life of one of them on Wednesday afternoon.
By establishing the circumstances of the pileup, investigators must include the SQ determine why the driver of the tractor-trailer was not able to brake in time to avoid the collision.