It was reported four vehicles, including an Audi, a BMW, and a VW Passat, were in collision shortly after 10.10pm on Saturday 26 September.
A woman who was a passenger in the Audi has sustained serious, potentially life-threatening, injuries.
The fourth vehicles failed to stop at the scene of the collision and we need to trace that vehicle and speak to the driver.
At this stage we do not have a description of the vehicle
We need to speak to anyone who saw what happened or has dash cam footage of it.
In particular we need to speak to anyone who saw how the Audi and another vehicle were being driven and interacted in the moments before the collision took place.
The southbound carriageway has been closed between junction eight for #Stansted and junction seven for Harlow while we carry out our investigations.
We expect the road the remain shut into Sunday morning so please avoid the area and plan your journey.
If you saw anything, have any dash cam footage, or have any other information we need you to call Police on 101 quoting incident 1337 of 26 September or Crimestoppers anonymously on 0800 555 111.