Around 50 homes have been cordoned off and a 55-year-old local man arrested on suspicion of possessing explosives for an unlawful purpose in Mexborough, South Yorkshire.
Supt Liz Watson said the incident seemed unlikely to be terrorism-related and it was possible the suspect was intending to make fireworks:
"We had some information that [the suspect] purchased some materials that could be used to make explosives. We've got specialist experts, military bomb disposal experts looking at the powders and substances. We think it's a case of someone who's been making fireworks."
An army bomb disposal unit and firefighters are at the scene in Chestnut Grove and residents have been taken to a local day centre by Doncaster Council until it is deemed safe for them to go home.
Supt Watson paid tribute to the way the community had responded to the incident: "I'd like to personally thank residents for their continued patience whilst we conduct our investigation. The community spirit has been second to none as up to 50 homes have been evacuated," she said.
"I'd also like to thank Doncaster Council and Highwoods Pub for all that they have done in supporting those residents during this period. We hope to have everyone back in their homes in time for tea and will keep you posted."