Public Health England are working with North Yorkshire County Council to investigate an outbreak of Covid-19 at a workplace in the county.
On-site testing is being offered at a company in Selby in order to identify additional cases and limit the spread of the virus.
The case rate in Selby has risen in the last week with over 50 new cases being discovered, which has sent the rate per 100,000 people in the area to 111, the average in England is 19.
It means that Selby now has the highest rate of Covid-19 in the UK.
Louise Wallace, North Yorkshire’s Director of Public Health said: "The company is working very closely with us as we take every measure, including workforce testing on-site, to contain this outbreak.
"As a consequence, we know that local infection rates will appear higher and show a short term increase before they start to drop again.
"However, this outbreak only serves to highlight that Covid-19 is still circulating among the population and shows how easily the rate can spike.
"So, as lockdown eases, we must all make every effort to follow the guidance around hands, face, space and fresh air, as well as taking up vaccination when it is offered."
Health officials have said they will also be tracking cases to ensure there is reduced spread in the community.