A man has been arrested by counter terrorism officers after bomb disposal experts were called to a house.
The 25-year-old is being held on suspicion of making or possessing explosives and having a gun following the incident in Basingstoke, Hampshire.
Army bomb disposal officers spent Thursday afternoon at the property in Penny Black Lane, in Rooksdown, where surrounding homes were evacuated.
Police have urged residents not to be alarmed.
Hampshire Constabulary said the man was initially arrested on Wednesday for possessing a firearm without a certificate.
He was arrested again on Thursday on suspicion of making or possession of explosives under suspicious circumstances, and on suspicion of possessing Class A drugs, officers said.
He remains in custody.
Hampshire police said a number of properties had been evacuated while specialist officers carried out searches, but there was not thought to be a wider threat to the public.
Ch Insp Matthew Reeves, district commander for Basingstoke and Deane, said: "You may notice an increased police presence, please don't be alarmed, officers are involved in the investigation and are there to assist and support."
The investigation is being led by Counter Terrorism Policing South East.