The incident happened between Junction 29 (Hornchurch) and Junction 28 (Brentwood, A12) at 12pm today (December 12).
The clockwise carriageway reopened at 3pm today with one lane closed, but the anticlockwise side remains fully shut.
National Highways Traffic Officers and area crews are assisting at the scene and managing traffic.
Vehicles trapped within the closure are being turned and released from the back of the queue.
Drivers face severe delays, with up to three hours reported on approach to the anticlockwise closure at Junction 29 and approximately 12 miles of congestion.
Diversion route for anticlockwise traffic:
Follow the Hollow Triangle diversion signs: Exit the M25 at Junction 28 and take the 4th exit onto the A12 towards London.
Follow the A12 to the Gallows Corner junction.
Take the 4th exit onto the A127 towards Southend.
Rejoin the M25 via Junction 29.
Motorists are urged to allow extra journey time, consider alternative routes, or delay travel where possible.
