Bomb disposal experts are investigating items found at a property in Plymouth as a number of homes are evacuated, police say.
Officers carried out a warrant at a property in College Avenue on Tuesday morning, where a white British man was arrested on suspicion of possessing a firearm without a certificate.
The 26-year-old remains in police custody.
Devon and Cornwall Police evacuated 259 properties while a cordon was put in place. It was lifted later in the evening.
Plymouth City Council set up an evacuation assembly point for households affected by the cordon at the Mutley Community Hub at the rear of the Mutley Baptist Church.
The incident is not believed to be terror-related, and there is not thought to be any wider risk to the public.