A 37-year-old man has been arrested under the Terrorism Act, police said.
The man was detained by officers in Penwortham, Lancashire, at 7am.
Police said there was no immediate threat and the arrest was not linked to Islamic extremism.
The joint operation involved Lancashire Constabulary and the North West Counter Terrorism Unit.
A spokeswoman for Lancashire Police said: "At approximately 7am this morning, a 37-year-old man in Penwortham was arrested under the Terrorism Act 2000 as part of a joint operation involving Lancashire Constabulary and the North West Counter Terrorism Unit.
"Specialist officers will be searching an address on Woodville Road in Penwortham and this will be done with sensitivity and carried out as quickly as possible to ensure minimum impact for local residents.
"Local officers with knowledge of the communities will be on duty in and around the area where the search is taking place and nearby residents will be receiving information in the form of a leaflet throughout the day."
Read More
MORE ABOUT