Restrictions put in place in Kildare, Laois and Offaly could apply to other areas in the future, Ireland's acting chief medical officer has said.
Residents are not permitted to travel beyond those counties except in limited circumstances.
The restrictions, announced on Friday in response to a spike in cases of Covid-19, came into effect at midnight.
Cafés, restaurants and bars have been closed, and there will be no sporting events.
Cinemas and gyms were also closed under the restrictions, which will remain in place for two weeks.
"It won't take much for other regions to have a problem as well," Dr Ronan Glynn told RTÉ.
"We need everyone to be cautious and follow public health guidelines."
The nation press