Traffic has ground to a halt on the M1 near Hendon and Harrow as it remains closed between two junctions further down the motorway.
Hertfordshire Constabulary received calls from concerned motorists after being concerned about two people on a bridge between Junction 5, Watford and Junction 6, Bricket Wood.
The ambulance service, police and air ambulance are all at the scene and the roads were closed earlier this morning.
It has caused congestion northbound to Junction 4 and the A41 at Edgware Way, and near Junction 2, Hendon.
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