A man is undergoing life-saving surgery after he was attacked and stabbed in the neck on Warner Bros set near Watford in Hertfordshire this afternoon.
The man who is understood to be a member of the film crew was treated by on-site medics and rushed to hospital following the incident.
Police say that they have arrested a 54-year-old man who is known to the man.
Warner Bros has said that they are aware of an internal despite claiming that it is an isolated workplace incident they are working with Hertfordshire police.
A spokesman for the force said officers had responded to a call from the Leavesden studios, where the Harry Potter series was filmed, just after midday on Wednesday.
One man was taken to hospital with a neck injury, while another was detained and arrested by officers who attended on suspicion of wounding with intent to do grievous bodily harm. The man remains in police custody.