Traffic is building up on the M25 after thick smoke from a lorry fire blew across the road.
The fire brigade is responding to the fire between junctions 22, for London Colney, and 21A, for St Albans, on the anti-clockwise carriageway.
Three appliances from Potters Bar, Borehamwood and Garston are in attendance.
Traffic was stopped on both carriageways at about midday due to the fire.
The smoke could be seen from Watford.