Counter terrorism officers are searching a house in the Lancashire town of Nelson.
Specialist officers from the North West Counter Terrorism Unit began the search at 7am at the property on Tavistock Street.
No arrests are planned at the address or elsewhere at the moment, according to Lancashire Police.
The search is being carried out using powers under the Terrorism Act 2000.
A Lancashire Police spokesman said: "At 7am on Thursday, October 1 2009, a search began at a property on Tavistock Street in Nelson under Schedule 5 Part 1 Paragraph 1 of the Terrorism Act 2000.
"No arrests are planned to be made at the address or elsewhere at this moment in time.
"Specialist officers from Lancashire Constabulary and the North West Counter Terrorism Unit will be searching the address 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."
