Around 100 homes were evacuated today after suspected explosive materials were found at a house.
Police made the discovery in Donnington, Telford, Shropshire, while conducting a search warrant, and a number of firearms were also found.
A spokesman for West Mercia Police said: "Explosives experts are currently at the property and a cordon has been established to protect the public. As a precautionary measure, around 100 homes in the immediate vicinity of the property are also being evacuated."
Detective Chief Inspector Jason Wells from Telford CID said: "We apologise to local people for any disruption this may cause them, but you will understand that we need to ensure the public's safety while we continue to deal with this incident.
"We are working closely with our colleagues at Telford and Wrekin Council to provide accommodation for anyone who has been evacuated from their home today and is unable to make their own arrangements for somewhere to stay.
"Transport is being provided to take people to a rest centre which has been established at Wellington Leisure Centre.
"At this time, officers are continuing to work at the scene alongside explosives experts to establish what, if any, explosives are present and to ensure that the area is made safe.
"In the meantime, I would urge people affected by this incident to listen to local radio for the latest updates or, if they require further information, to call West Mercia Police on 101."
It is expected that the cordon may be in place for at least the next several hours and possibly longer into the day, the spokesman said.
A man in his 40s has been arrested in connection with the incident and is being questioned by detectives.