An armed police officer accidentally fired a weapon inside Exeter Police station, damaging a nearby patrol car.
The incident is understood to have happened two weeks ago at the Heavitree Road station while the officer was unloading his weapon.
The officer, who has not been identified, has been removed from firearms operations.
Police, who are investigating the incident, said one round of ammunition was discharged a year.
Safety 'paramount'
Supt Richard Baker of Devon and Cornwall Police, said: "Incidents such as this are very rare and are treated seriously.
"Safety is paramount and the force will look to see if any lessons can be learnt from this incident."
He added: "Thousands of rounds are safely loaded and unloaded and, on average, only one round is accidentally discharged each year."
The investigation is to establish exactly what happened and whether force procedures were being followed. The Home Office has also been informed.
A spokesman for the force said: "Devon and Cornwall Constabulary confirm that there has been an accidental or unintentional discharge of a firearm within the confines of Heavitree Road Police Station.
"No-one was injured but damage was caused to a police vehicle."