Officers remained at a building on Yoden Way in Peterlee on Friday, January 14, and are expected to be present for some time following the discovery on Thursday, January 13.
Representatives from County Durham and Darlington Fire and Rescue Service and NEDL have attended to ensure the premises is safe.
11 of the most mispronounced place names in and around Hartlepool
Watch as a big explosion completely demolishes Sinter Plant
Met Office announces yellow weather warning for thunderstorms across North East following heatwave
Plea to trace family of Hartlepool man in his sixties who died this week
Police appeal to find missing 40-year-old last seen in Billingham
Inspector Gary Smith, of Peterlee Neighbourhood Policing Team, said: “The scene has been secured and members of the public may notice an increased visibility of police in the area for some time while we carry out further enquiries.
“However, we would like to stress that while there will be a significant presence of officers in the area, there is nothing for the community to have concerns about”.