Officers from Herts Police have launched an investigation following a life changing collision.
London Road in St Albans is closed following a serious traffic collision which happened at 1.35pm this afternoon.
Drivers carrying out essential journeys are asked to find alternative routes.
Police, fire and ambulance and air ambulance are in London Road following the collision which happened near Cunningham Avenue by the railway bridge.
A marked police car, which was responding to an incident, overturned after hitting a brick wall.
The police officer has serious injuries and has been taken to hospital by air ambulance.
No-one else was injured.