Police have closed Pinner Road northbound after a serious accident involving a pedestrian and a bus outside Bushey Station.
The road has been closed since midday as police, fire and ambulance crews deal with the incident.
The accident took place between Oxhey Avenue and the A411 Lower High Street, A4125 Eastbury Road and Chalk Hill junction.
Buses heading towards Watford town centre are on diversion via Falconer Road, Finch Lane, The Avenue, Aldenham Road, A41 and A4008 Stephenson Way.
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