Armed officers were called to assist as police searched a house in Rushden.
Road cordons were put in place while a search was carried out at a house in Highfield Road in the town this afternoon.
A spokesman for the force said it was part of a planned police operation and it was expected that officers would remain at the scene for several hours this evening (Wednesday).
The spokesman said: “Officers have searched a property in Highfield Road, Rushden.
“We entered the building at about 4pm and the operation inside the property is likely to continue for some time.
“We would like to reassure residents of Rushden that this is a contained operation and there is no need for members of the public to be concerned.”
The spokesman said they were unable to provide any further details at this time.