A SUB-machine gun with ammunition fell out of a Garda car after it went over a ramp and the boot opened.
An investigation has been launched after the firearm went missing for a time in Dublin before being later handed into a station.
The incident happened at around 6pm on Tuesday at Harcourt Square.
Officers in the car saw the incident happen and witnessed the gun being picked up. They pulled over but the person and bag with the gun in it had gone.
The Heckler & Koch MP7, was handed into Store Street Garda Station 25 minutes later.
The weapon is not understood to have been fired and all the ammunition was accounted for.
A senior Garda officer has been appointed to examine the circumstances. This will include an examination of the mechanics and road worthiness of the car and a review of security procedures.
Justice minister Charlie Flanagan said the incident as a matter of grave concern.
"It appears a machine gun fell out of the back of a car and was handed in by a very civic-minded citizen into the gardaí. So luckily any danger was averted," he told RTÉ.
"The issue is currently the subject matter of an investigation by a chief superintendent. How it might have happened. How it did happen?"
