A controlled explosion was carried out early today after a man was arrested under the Terrorism Act, police said.
About 30 people were evacuated from their homes in Westbury-on-Trym, Bristol, during the operation.
A 19-year-old from the area was arrested in connection with the investigation yesterday afternoon.
Assistant Chief Constable Jackie Roberts said: "It was a controlled explosion and the materials will be sent off for analysis.
"We responded to intelligence given to us in the last 24 hours."
The suspect was being questioned today at an undisclosed police station.
Ms Roberts said it was too early to say if any more arrests would be made.
The controlled explosion, carried out at 2am, also involved the Metropolitan Police.
Ms Roberts added: "During yesterday and overnight, Avon and Somerset Constabulary have been co-ordinating a number of covert inquiries.
"As a result, a 19-year-old man was arrested yesterday afternoon under the Terrorism Act 2000.
"He has been taken to a police station within the force area and a warrant was executed to search his home in the Westbury-on-Trym area.
"A number of people were evacuated from neighbouring homes as a precaution, and just after 2am this the morning the Explosives Ordnance Disposal Team conducted a controlled explosion at the location."
She said police were continuing to liaise with various "relevant agencies" to further the investigation.
She added: "This is likely to be a prolonged, complex and sensitive inquiry which may take some time."
Police would not reveal what sort of materials were blown up in the early hours but said they had now been sent off for analysis.
The house, in Comb Paddock, a cul-de-sac on the border of the Southmead area of Bristol, was likely to be cordoned off for the remainder of the day.
Ms Roberts added: "We would like to reassure people that this arrest has been made to prevent harm.
"It is unlikely that those who have been evacuated will be able to return to their homes until much later today at the earliest."Reuse content