Britain's busiest motorway has been hit with long tailbacks following the incident on a stretch of the road in Hertfordshire, which has left one man fighting for life in hospital.
The stretch of road shut is the M25 between junction 23 at South Mimms and junction 25 at the junction with the A10 north of Enfield.
Crash: A lorry has overturned in the middle of the M25 in Hertfordshire, injuring four people
It is expected to remain closed throughout the Friday evening rush hour, raising the possibility of chaos on the roads around London.
Police, firefighters and ambulance teams all attended today's incident which was between junction 24 at Potters Bar and junction 25.
Four men were taken to hospital by the London Ambulance Service - one is in a critical condition, another is suffering from serious injuries, and two more have minor injuries
No other vehicles were involved in the crash.
Chaos: This traffic map shows how the closure has brought gridlock to surrounding areas
Around midday, the Highways Agency said the closed section was likely to stay shut for most of the day. Motorists were asked to consider alternative routes.
Police said that two other men had been hurt in today's accident. Both had been taken to hospital for the treatment of minor injuries.
There were severe delays on the northern part of the M25.
On Tuesday, the M25 had to be closed between J23-25 after the driver of a lorry died when the vehicle overturned and caught fire near J25.
