Lockdown restrictions are to be put in place for Kildare, Laois and Offaly from midnight.
This will see pubs and restaurants operate as takeaway only.
However shops can remain open and trading, but must adhere to face covering and social distancing guidelines.
Childcare and schools that are open can also remain open - while preparations to re-open schools will continue.
People in those counties are being asked to restrict their movements to within their own county.
The restrictions will be in place for a period of two weeks.
People are also being urged to avoid all non-essential travel during that time.
Households there are being asked to restrict visitors to six people from no more than three other households.
While nursing home visits and visits to prisons are suspended, except on compassionate grounds.
Non-contact sport can take place in groups of no more than 15, while contact sports are suspended for the two week period.
Those who can work from home should do so - with employers being asked to facilitate this in every way possible.
Other amenities - such as cinemas, museums and bingo halls - will be closed.
People will be able to travel through these counties to get to other destinations as normal.
However people who do not live there are being asked to not travel to the three counties, unless it is for work or essential care for a relative.
A special Government web page has been created to advise people living in those areas.
Addressing the nation earlier, Taoiseach Micheál Martin said:"We have now seen an increase in cases in our own country.
"We are still doing very well by international standards - but over the past week, there have been a number of localised clusters which are a serious concern".
"We have to be decisive, we can't afford to wait and see - the disease is not waiting.
"We must protect public health to the greatest extent possible, everything else is secondary to that.
"And if this requires difficult decisions, then so be it."
He added: "We know that we could go further in terms of restrictions, but we are conscious that as we move forward through this pandemic our responses need to be more nuanced and more sustainable.
"We also believe that the vast majority of people understand that we are in this together and they will do as they are asked.
"I am also asking everyone else in the country to do two things.
"Firstly, do not to travel to these counties unless for the purposes of work or essential care for a relative.
"Secondly, please pause and reflect on what else you can do, what your friends and family can do, and what your colleagues can do, to slow the spread of this disease."
Extra HSE resources
The Health Service Executive (HSE) is to provide additional resources, particularly in their contact tracing work.
The National Ambulance Service has been mobilised to provide additional pop-up testing facilities in the region from Saturday.
And its regional community response teams will provide communications and support to long-term residential care facilities in Laois, Offaly and Kildare - including all nursing homes, both public and private.
It will also be providing isolation facilities for those who cannot self-isolate in their homes or communal settings.
HSE chief executive Paul Reid said: "We have worked so hard as a people to suppress this virus.
"Our success to date in containing the spread of this virus has been as a result of the solidarity of all of our people in following public health advice.
"We all need to redouble those efforts now, particularly in the three counties worst affected.
"I want to urge everyone to continue to wash their hands, maintain social distance, wear a face covering on public transport and in shops and sign up to the COVID App.
"If you have any symptoms, or are a close contact of a case, please come forward for a test.
"The people of Laois, Offaly and Kildare I know will be particularly disappointed tonight to be taking a step back.
"I want to assure them that the HSE will continue to bring every resource at its disposal to support them in reducing the spread of COVID-19."
It comes after 226 cases have arisen in Kildare, Laois and Offaly over the past 14 days.
Acting Chief Medical Office Dr Ronan Glynn said imposing the regional lockdown will help to control the disease.
He said while these decisions are not easy, we need to remember that no one is immune.
"NPHET believes that this package of measures of measures today represents a proactive and proportionate response to the evolving situation.
"I fully understand that today's decision will be very disappointing and will cause significant disruption for many of the people in these counties who have already made very significant personal sacrifices".
Meanwhile a food factory in Co Kildare, which suspended all operations after it identified 80 confirmed cases of the virus, has reported several more.
O’Brien Fine Foods in Timahoe also said there appeared to be a "very high" level of asymptomatic infection.
In an updated statement on Friday, the company said six more cases were found to be positive for COVID-19.
It said: "Those who have tested positive have been advised to isolate as per the official guidance.
"Full risk assessment and contract tracing procedures is continuing.
"All close contacts of those affected are being notified, advised to self-isolate and to contact their GP."
The company added that it has operated a "rigorous" health and safety policy since February.
This included working from home for all non-operations staff, mandatory PPE, Perspex screens, staggered shift and break times, restricted visitor to site policy and daily temperature checking.
"Given this level of rigour and our comparatively low level of confirmed cases up to this point, this sudden spike is difficult to comprehend", the company statement added.