Seven workers at a chicken processing plant have tested positive for coronavirus and five more are isolating as they await test results.
The outbreak at Banham Poultry in Attleborough, Norfolk, was announced by Louise Smith, the director of public health at Norfolk County Council.
Ms Smith said more staff at the site would be tested.
She said the plant, where several hundred people work, had acted quickly to prevent the spread of the virus.
The council has been working with Public Health England, the NHS and Breckland Council.
Ms Smith said Banham Poultry’s management team was working closely with the county council to trace the contacts of those who have tested positive.
“We are monitoring the situation and taking action to prevent further transmission both at the site and in the community,” she said.
“Testing of a further number of staff is being arranged at the Banham Poultry site… as a precautionary measure.”
Blaine van Rensburg, managing director of Banham Poultry said: “The safety of our staff, customers and the wider public is really important to us and we are working with public health authorities to make sure we are doing absolutely everything we can and following all of the correct procedures.
“The business remains open and operating and we are doing everything we can to prevent the further spread of the virus.”