The Department of Health has been notified of 4,962 new coronavirus cases and seven further deaths.
It brings the number of Covid-19 cases in Ireland to 101,887 while the number of people who have died with the virus has reached 2,259.
Of the new confirmed cases, 2,408 are men and 2,539 are women.
There are 62 people in intensive care with Covid-19, this is a rise of six since yesterday. There are 685 people in hospital with the virus, with 96 additional hospitalisations in the last 24 hours.
In a statement, the National Public Health Emergency Team says that the median age of the new cases is 36, while 63% are under the age of 45.
NPHET says 1,260 of the cases are in Dublin, 652 in Limerick, 350 in Cork, 321 in Louth, 238 in Meath and 2,141 spread across all remaining counties.
The 14-day incidence rate is now 469.8 per 100,000 of population.
Counties with the highest rates of infection include Monaghan (1,060.5), Louth (941.2) and Limerick (895.3).
Those with the lowest rates are Wicklow (195.2), Tipperary (250.7) and Kildare (277.3).
The Deputy Chief Medical Officer has appealed for people to stay at home and follow the Level 5 guidance.
Speaking on RTÉ's Six One News, Dr Ronan Glynn said tomorrow is the day when people return to work, but they need to stay at home and employers need to facilitate that.
"We need to do all we can to make sure as few further people as possible get infected," he said.
"To do that, we need every single person across the country to act as if they are infectious – to cut their contacts. Tonight I am asking people to cut their contacts to all, but those are absolutely essential over the coming week."
Dr Glynn said that while the Covid-19 vaccination programme is a reason for hope this year, it will not stop people from becoming sick over the next week or the next two weeks.
"A vaccine will not stop anyone becoming sick over the coming days and we need everyone to act as if it's last March, to protect themselves their families and in particular for those who are older and who have medical conditions," he said.
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The Chief Medical Officer has said that the increase in the number of Covid-19 cases is deeply concerning, and people must work together to address the issue as quickly as possible.
Dr Tony Holohan said that this is a "critical time".
Dr Holohan said: "We are seeing a really significant surge in infection, which is leading to a very rapid increase in both hospitalisations and admissions to critical care units.
"This is not only unsustainable for the healthcare system, but also a deeply concerning level of preventable sickness and suffering that we must work together to address as quickly as possible.
"The number of people in hospital with COVID-19 has more than doubled from this day last week, and so has the number of people in ICU. Remember that behind each hospital statistic and ICU figure is a real person like you, with a family who cares about them, and a team of healthcare workers dedicated to protecting their lives.
"We must be as dedicated as we all were in the spring in our commitment to following the public health advice."
"Act as though you are infectious. Stay at home. Work from home starting from tomorrow, and if you are an employer, ask your employees to work at home. What we all do at a collective level today will have a direct impact on the level of infection and hospitalisations in the weeks to come."
Covid-19 numbers 'difficult to cope with' - INMO
The Irish Nurses and Midwives Organisation has said hospitals are under "extreme" pressure and the progress on keeping case numbers down "seems to be completely undone".
INMO General Secretary Phil Ní Sheaghdha said that although staff are far more experienced in dealing with Covid-19 than they were at the start of the pandemic "the sheer numbers are difficult to cope with".
She said the Government and the Health Service Executive "must focus on supporting exhausted frontline healthcare workers".
Ms Ní Sheaghda said that over 100 nurses at Cork University Hospital are out for Covid reasons, including in the intensive care unit, and one ward has been closed as there were only four nurses available to staff it.
CUH is urging people not to attend its emergency department unless absolutely necessary.
In a statement, the hospital said the ED is exceptionally busy today due to a large number of very ill patients.
It has asked people to contact their GP/South Doc, the Mercy Urgent Care Centre or local injury units at Bantry or Mallow if possible before attending the emergency department.
Tánaiste Leo Varadkar said the situation is alarming and he could not rule out more restrictions.
Speaking on RTÉ's This Week, he said the current rules must be given time to work.
Taoiseach Micheál Martin has said that with Covid case numbers rising rapidly people should stay at home and strictly limit their social contacts.
In a tweet, he said: "We must do everything we can to protect the most vulnerable and those on the frontline".
With Covid case numbers rising rapidly, it's more important than ever that each and every one of us does what is being asked of us.— Micheál Martin (@MichealMartinTD) January 3, 2021
Stay home and strictly limit social contacts.
We must do everything we can to protect the most vulnerable and those on the frontline.
Chair of the National Public Health Emergency Team Epidemiological Modelling Advisory Group Professor Philip Nolan said the rate of growth in Covid-19 cases is a "major concern" and warned of further increases "before we turn this around".
We see further increases in numbers in hospital (673) and ICU (62) this morning. The rate of growth is a major concern and there will be further increases before we turn this around. A clear signal to all of us of the need to protect ourselves and each other by staying home. pic.twitter.com/zuLP5KzYuA— Professor Philip Nolan (@President_MU) January 3, 2021
NPHET has said case numbers could rise further, warning that up to 6,000 a day could be seen at the peak of the current wave.
Covid-19 case numbers have been artificially low in the past week, as the IT system used to notify confirmed cases struggled to cope with huge numbers of positive test results.
A backlog of around 9,000 positive cases, is now being cleared and is part of the reason the latest figures are so high.
Additional reporting Fergal O'Brien and Orla O'Donnell