A crash on the Eastbound 401 in Ajax is snarling traffic east of the city.
Three tractor trailers were involved in the crash near Harwood Avenue around midnight.
The OPP says one tractor trailer rear ended 2 others that were stopped because of construction ahead.
One driver has been taken by air ambulance to hospital in critical condition.
Just one lane is open past Westney as emergency crews work to clean up the mess.
Sergeant Dave Woodford says the clean up could last up to the morning rush but they are hoping to open up 2 lanes by 4am.