The "steep rise" in cases in the High Peak area is "deeply concerning" but not "surprising", Derbyshire's public health boss has said.
Parts of High Peak will be put under "tier two" and placed on "high" alert from Wednesday.
Derbyshire County Council said the infection rate in the Glossopdale area is the highest in the county at 294 per 100,000 people.
The authority has urged residents to avoid household mixing indoors, adding that outdoors, people should stick to the "rule of six".
It added people in the area should only travel if it is essential.
Dean Wallace, the county's director of public health said there is "a lot of community transmission" in the area.
He added: "The steep rise in the numbers of cases is deeply concerning, although not surprising given the close proximity to areas which have been under extra restrictions for a while, so it's more important than ever that we all work together to beat this."