Hampshire police received a report at 6.45pm yesterday of a man brandishing a firearm in Twyford Avenue in Stamshaw.
Officers have reassured the generally public that they take this type of report extremely seriously.
An armed response unit was deployed to the scene as a precaution to safeguard the community. An imitation firearm was seized at a Twyford Avenue residential address.
A 35-year-old man from Portsmouth was arrested on suspicion of possess an imitation firearm in a public place.
If you have any information relating to this case, please call Portsmouth police on 101 quoting reference 441 8008 3092, or contact the Crimestoppers charity anonymously.