A city-centre building site has temporarily closed on HSE advice after more than 20 cases of Covid-19 were detected among workers there.
Up to 200 staff were working on the site, and those who came into contact with the workers are being urged to get tested as soon as possible to prevent the virus from spreading further.
The site was shut temporarily after advice from the Health Service Executive (HSE) yesterday.
Further tests on staff are being carried out. John Paul Construction has confirmed a number of its building workers at the site had contracted coronavirus.
There are fears over the infection rate due to the large number of people on site.
The building site in Townsend Street, Dublin, is being developed for a 393-bedroom hotel, 202-aparthotel, a restaurant, along with 21 apartments.
Acting chief medical officer Dr Ronan Glynn described it as "the first significant outbreak" on a construction site to date.
"I really want to use this as a signal to employers to look at what you and your staff are doing," he said.
It is understood one employee was initially diagnosed with Covid-19 at the latter end of last week.
Comprehensive testing was carried out once the company became aware of the positive case and a number of other staff have since tested positive.
Labour councillor Kevin Donoghue described the outbreak as "very concerning".
He has called for testing to be made available for locals and shop workers in the area who may have come into contact with the staff from the construction site.
"The workers on the site would have been using shops locally during breaks and we need to be ready to test local residents who might be impacted by this," he said.
"Measures should be put in place to allow all residents in the area who are concerned to get tested immediately.
"In their statement the construction company involved said comprehensive testing of workers had been carried out after one person tested positive for the virus. We need to ensure that testing is made available for locals also, especially where they may be concerned about at-risk family members."
In a statement, John Paul Construction, which has offices in Dublin, Galway, Cork, London and Riyadh, said: "We have followed the specific advice of the HSE and the Health and Safety Authority at all times in relation to this matter and are assisting the HSE in arranging further tests as required. We have temporarily closed the site.
"The health, safety and wellbeing of those who work with us and the communities in which we operate is our top priority and we wish those affected a speedy recovery."
The situation has been described as "fluid" and staff are due to be retested next week.