Twenty-one people have now tested positive for coronavirus at a caravan park site in Craven Arms, Shropshire and health experts have warned that number will rise
Two positive cases were confirmed at Craven Arms last week, linked to an outbreak in Welshpool and a recent local event.
A testing site has now been set up at a nearby business park and all residents have been told to self-isolate with their families.
To date 41 people at the residential site have been tested.
Contact tracing is being undertaken, and the number of positive cases is expected to increase before infection control measures and social distancing start to take effect, the council said.
Those who tested positive were asked to isolate for a minimum of seven days from the time they started showing symptoms, or from when they took their test.
The council says people who were in contact with a positive case were told to isolate for 14 days.
A playground and outdoor gym on nearby Newington Way has been temporarily closed to help stop transmission, and the council said it had been arranging the delivery of food, prescriptions and essential supplies for residents.