The crash occurred close the Holmesdale Tunnel near Waltham Abbey.
Two lanes are currently closed amid reports of five to seven miles of traffic.
The tailback stretches from J26 for Waltham Abbey all the way to J27 for the M11.
Essex Travel News tweeted: “M25 Anticlockwise – Accident involving a lorry and a car blocking two lanes in the Holmesdale Tunnel (between J26 (Waltham Abbey) and J25 (A10).
“Queuing traffic back towards J27 (M11).”
More to follow…