Public Health Wales says it has identified 58 confirmed cases of Covid-19 linked to a poultry processing plant on Anglesey.
All employees at the Llangefni 2 Sisters poultry processing factory in Llangefni have been told to self-isolate.
Earlier, the plant said it was closing the site for two weeks to “clearly demonstrate how seriously we take this issue”.
2 Sisters Food Group is one of the largest food producers in the UK, with brands including Fox’s Biscuits and Holland’s Pies.
Public Health Wales said: “We are working in close collaboration with the employer and Anglesey Council, and our priority is to bring this outbreak to a swift conclusion.”
The outbreak of Covid-19 at a chicken factory on Anglesey “reiterates the importance of social distancing and hand hygiene”, Wales’ health minister Vaughan Gething said.
Speaking at the Welsh Government’s daily press briefing, Vaughan Gething also said he was “concerned” there may be more confirmed cases to come.
“Obviously this reiterates a number of points: it reiterates the fact that even with a low prevalence of coronavirus it hasn’t gone, it reiterates the importance of social distancing and appropriate hygiene measures, it also reiterates the importance of our test trace protect system,” he said.
“People really do need to follow the advice that they’re given on getting a test, and on self isolating.
“Given that this is a closed setting in which these people would have been working, I’m obviously concerned that we may well see more confirmed cases of coronavirus,” he added.