One person is in a serious condition and has been flown to the Royal London Hospital by Essex and Herts Air Ambulance, after a crash on the M25 near Potters Bar this afternoon.
Traffic has been now released at J25 to J24 anti-clockwise as the air ambulance - which was called at 1.48pm - has now taken off.
The East of England ambulance service sent the Hazardous Area Response Team, two ambulance officers, a rapid response vehicle and one ambulance to the scene.
The M25 J24 to J25 clockwise carriageway is still closed, according to Highways England.
It advised that if you are heading clockwise, there is just under seven miles of congestion on approach to the carriageway closure at J23, and anti-clockwise there is two and a half miles of congestion on approach to J25.
The A1(M) is also dealing with severe congestion after two lanes on the entry slip at Junction J23 were closed.
Updated diversion details can be found at m.highwaysengland.co.uk/#news.
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