Public Health Wales has told staff who work at a chicken processing plant to self-isolate after there were 58 confirmed cases of coronavirus at the site.
Production at the plant which has contracts with Marks & Spencer and KFC has been shut down for a fortnight.
A testing facility has now been set up in Llangefni, and an existing facility in Bangor is also being used. A further facility is also being set-up in Holyhead to test all staff.
Earlier this week unions said they were aware of cases among staff at the 2 Sisters factory in Llangefni, with 110 people self-isolating as a precaution, while council chiefs said efforts to tackle the cluster were being "treated as a priority."
On Thursday, the 2 Sisters Food Group announced it was "doing the right thing" and would cease work on site for 14 days with immediate affect.
In a statement, the firm said: "The health, safety and wellbeing of our colleagues is ultimately the thing that matters most at our business. We are a responsible company with people at its core. Without our people we are nothing.
"Therefore in light of the current Covid-19 cases at our Llangefni site, we have decided to take the necessary action to clearly demonstrate how seriously we take this issue by doing the right thing.
"Doing the right thing means from today we will temporarily suspend production at our Llangefni site with immediate effect for a period of 14 days.
"We will not tolerate any unnecessary risks - however small - for our existing loyal workforce at the facility.
"We have worked in close collaboration in the past week with Public Health Wales, Anglesey Council, the Health & Safety Executive, the FSA (Food Standards Agency) and the Unite union who have all offered great advice, scientific knowledge and support, and we thank them for their help and guidance which has informed this decision.
"Our sole focus now is to ensure we support all our colleagues through this time and look forward to operating safely and securely in 14 days' time."
Health minister Vaughan Gething said the situation reflects the importance of good hygiene.
"Given this is a closed setting - I am concerned we may well see more cases of coronavirus.
"I'd ask people to recognise the seriousness of coronavirus, the need to follow the guidance, get a test and follow the advice from Test, Trace, Protect."
Member of the Senedd for Ynys Môn Rhun ap Iorwerth said it was the "correct decision to safeguard staff and the public."
Dr Christopher Johnson, Consultant in Health Protection for Public Health Wales, confirmed that staff had been told to self-isolate for two weeks.
We would remind all members of the public that they have a vital role in preventing the spread of Coronavirus, to help keep Wales safe.
“Public Health Wales can confirm that employees and contractors of the 2 Sisters poultry processing plant in Llangefni have been notified that they are Coronavirus contacts, and we are asking them to self-isolate for 14 days to help protect population health," he continued.
“We are working in close collaboration with the employer, Anglesey and Gwynedd Councils, Betsi Cadwaladr University Health Board and other partners, and our priority is to bring this outbreak to a swift conclusion."
The company has not confirmed the number of coronavirus cases but said the first reported positive case at the plant was on May 28 and that a full "safe ways of working" action plan had been in place since early March.
Production at the factory, where 560 people are employed, will be transferred to other company locations until July 2.
2 Sisters Food Group is one of the largest food producers in the UK, with brands including Fox's Biscuits and Holland's Pies, and customers such as supermarkets, KFC and Marks & Spencer.
Analysis by ITV Wales health reporter James Crichton-Smith
Expect more of this sort of thing in the future.
In many ways, what is happening to the 2 Sisters factory is like a hyper-local lockdown.
Production shut down, everyone told to isolate, contacts traced.
This is exactly the sort of scenario that the test trace and protect strategy would have anticipated, and will no doubt continue to expect as lockdown eases. Public health officials in Wales, as demonstrated in this case, will be extremely alert to outbreaks like the one seen at 2 Sisters. By taking decisive action at the first sign of a significant flare up of any outbreak, authorities will be hoping it is enough to stop this local outbreak from spreading.
Around the world, and notably in South Korea, comprehensive track, trace and isolate measures have ensured very few Covid-19 deaths and cases when compared to those in the UK. In China, where the outbreak started, significant local measures were taken this week in Beijing after traces of the virus were found in a market there. Like at 2 Sisters, the market was closed, staff told to isolate, extensive testing undertaken.
Here in Wales contact tracers, through their work, will flag up any trends that emerge. When a cluster becomes apparent, the system will be notified and targeted action will be taken.
The 2 Sisters case might be one of the first examples in Wales where action to stop production and tell all staff to self isolate is taken, but it's unlikely to be the last.