The A1(M) is currently closed southbound near Welwyn with long delays in both directions after a major crash.
The air ambulance is on scene after a serious crash on the southbound carriage way within Junction 6, which is believed to have involved multiple vehicles.
The northbound carriageway has reopened after it was temporarily closed to allow the air ambulance to land.
Motorists are urged to avoid the area and consider alternate routes as there are long delays of at least 40 minutes are expected between J7 (Stevenage) and J6 southbound and between J5 (Welwyn Garden City) and J6 northbound.
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