200 people have been asked to vacate their homes after a "potentially volatile" substance was found in a flat.
A substance was discovered during a search of the flat in Belvoir Crescent on Saturday afternoon.
Police are working with council emergency planners to move families from homes within 100m of the find in Newhall, South Derbyshire, as a precaution.
A 55-year-old man was arrested after Superintendent Paul Markham, who is in charge of the operation, said: "We are not looking for anyone else in connection with this matter and we are hoping that people will not be inconvenienced for too long.
"The evacuation is purely a precaution to ensure everybody's safety and residents will be allowed back home as soon as possible."