Northern sections of the M25 will remain shutdown in both directions until at least 2100, following a crash near Potters Bar.
The crash, in which four men were injured, occurred when a lorry overturned in the rush-hour at 9.18am. One of the men suffered potentially life threatening injuries and was flown by helicopter to Addenbrooke's Hospital in Cambridge.
This is the fourth accident on the same stretch of the motorway this week. On Tuesday a lorry driver died after his vehicle tipped over and caught fire.
The motorway is closed in both directions between junctions 24 (Potters Bar) and 25 (Enfield) and congestion is being experienced to junction 27 (M11) anti-clockwise and junction 21a (St Albans) on the clockwise carriageway.
Drivers are being advised to follow signs with a hollow triangle symbol for a diversion anti-clockwise or to follow the hollow square symbol signs for a clockwise diversion via the A1, A406, and A10.