Parts of two motorways have been closed following crashes that left two people badly injured.
On the M11, a woman suffered potentially life-threatening injuries in a smash involving four cars on the southbound carriageway near Harlow at about 10.10pm on Saturday.
An Audi, BMW and Volkswagen Passat were involved in the crash, along with a fourth vehicle which police say failed to stop at the scene. A description of the vehicle has not been given.
Essex Police said they expected the southbound carriageway between junction eight for Stansted and junction seven for Harlow will "remain shut into Sunday morning so please avoid the area and plan your journey".
The force said: "We need to speak to anyone who saw the collision or has dash cam of it.
"In particular we need to speak to anyone who saw how an Audi and another vehicle were being driven and interacted with each other in the moments before the collision."
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Meanwhile, the M1 in Leicestershire was closed at junction 23 near Loughborough in both directions after a crash just before 11.20pm on the northbound carriageway.
A rear passenger in a Range Rover has been left in a critical condition following the collision, which also involved a black Audi RS4.
The Range Rover driver and a front passenger were also wounded but their injuries were not thought to be life-threatening, police said. The Audi driver was not hurt.