Drivers are being warned of long delays and diversions following a serious collision between Junction 25 (Enfield) and Junction 27 (Epping, M11).
The M25 is closed clockwise, with National Highways warning that a "complex recovery is ongoing at the scene and is likely to be protracted".
It added that there is currently no estimated reopening time, with motorists urged to follow the diversion routes set up along the hollow triangle diversion symbol on road signs.
It is believed that two lorries and two cars were involved in the accident, with one person taken to hospital with injuries.
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The M25 is closed clockwise as a result of the accident
NATIONAL HIGHWAYS
Congestion maps from National Highways show miles of road where traffic is not moving, with adjacent roads seeing very slow moving traffic.
The transport organisation has warned that there are long delays on the approach, with an estimated time of 45 minutes clockwise above the normal time.
Similarly, there are delays of 30 minutes anti-clockwise with traffic moving slowly past the scene of the accident.
National Highways has estimated that the event will be cleared between 3.30pm and 3.45pm, although this is subject to change.
A similar timeframe has been given for when the transport authority has estimated that normal traffic conditions will return.
Essex Police said: “We were called to a collision involving four vehicles on the M25 at junction 26 clockwise, shortly after 5.30am this morning (Wednesday 26 June). Officers attended alongside fire and ambulance service colleagues.
“One casualty has been taken on to hospital with serious injuries, not believed to be life-threatening.
"A road closure remains in place at the scene while this incident is cleared and enquiries continue,” Essex Live reported.
Motorists have been advised to avoid the area if possible and seek alternative routes while the scene is cleared.
For drivers following the diversion route, they should exit at J25 and take the third exit at the roundabout onto the A10 towards London.
They are advised to then follow the A10 to “Great Cambridge Junction” and take the first exit onto the A406 “North Circular Road” towards the M11, Walthamstow and Edmonton.
Once they have reached J4 on the M11, they should keep in the middle lane and take the link road onto the M11 towards Cambridge.
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Traffic is building at the scene
NATIONAL HIGHWAYS
From here they can take the exit at M11 J6, M25 J27 and bear right to rejoin the M25 clockwise, National Highways detailed.