A local lockdown could be enforced on Anglesey to contain a coronavirus outbreak at a poultry factory.
Giri Shankar of Public Health Wales said "aggressive control measures" were being used on the Welsh island to stop the infection.
A total of 158 workers at the 2 Sisters meat processing plant have tested positive for COVID-19.
Staff are self-isolating and the factory has closed while all workers are tested.
Dr Shankar told BBC Radio Wales that local lockdowns could be something "we need to consider".
An outbreak team was established last week following the reported infections.
Dr Shankar said: "[We have] been meeting daily and advocating aggressive control measures so that we can halt the spread of the infection.
"At the moment all the employees at that particular factory have been offered testing.
"Of the remaining tests that are still out in the lab we still expect to see a further increase but all the control measures are in place.”
Welsh first minister Mark Drakeford has said he will not bring in a local lockdown on Anglesey yet – and revealed the test he will apply to determine if one is needed.
He said there would be "no delay" in bringing in a local lockdown if it was required but that it would be done in a proportionate way.
Drakeford said he met with leaders on the island on Monday morning and that the test, trace and protect programme was working well in identifying people with the virus.
He said: "The discussions are very serious but I want to remind people that it is an outbreak in a closed setting, amongst people who work in the factory. Our test, trace and protect system has been mobilised very vigorously."
Drakeford said the test for a local lockdown will be whether "there is significant seepage of the virus from the closed setting into the wider community".
He said: "You have to be proportionate. Decisions that restrict people's liberties should not be taken lightly. We won't take those actions until we know they are necessary for that purpose.”
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