A "toxic and unprecedented level of scenarios" have emerged as a result of the increase in COVID-19 cases, according to the CEO of the HSE.
Positivity rates for tests on some days are reaching as high as 20%, including on tests carried out yesterday.
It comes as the Cabinet is gathering to consider reintroducing level five restrictions, which would close non-essential retail and gyms.
The unscheduled meeting is taking place this afternoon due to the soaring rates of coronavirus in Ireland.
1,546 new cases were confirmed yesterday while 454 patients are currently in hospital today with the virus following 59 further hospitalisations in the last 24 hours.
The head of the HSE Paul Reid says the scale of which the virus is transmitting is worrying.
He told a HSE briefing this afternoon that most of his worst concerns about the capacity of the health system which had been outlined before Christmas "have certainly been realised".
Mr Reid said: "There's what I describe as an unprecedented and toxic combination of potential scenarios [which] have literally been realised and have emerged.
"That's a combination of a massively high level and rapidly growing daily cases."
Added to this is high levels of positivity which "we haven't seen in such a long time" and "extreme" numbers of close contacts.
Colm Henry of the HSE says the R-number of COVID-19 transmission in Ireland is now at 1.8.
Earlier Paul Reid says they’re facing ‘toxic and unprecedented’ scenarios with positivity rates as high as 20% on some days.
— Andrew Lowth (@AndrewLowth1) December 30, 2020
Speaking at the same briefing, Dr Colm Henry, the Chief Clinical Officer at the HSE said the R-number of COVID-19 transmission in Ireland is now at 1.8.
Mr Reid said the HSE were extremely concerned about the number of hospitalisations, particularly in the past 48 to 72 hours.
He made an "urgent and serious call to the public" over the "alarming and high-risk situation" with the virus at the moment.
Transmission levels in the community are very worrying, he added, and so he called on "everybody to take immediate actions" over withdrawing from any planned activities involving meeting people in the coming days.
The average positively rate over the past seven days has been at around 10%, but on some days, including yesterday, that hit 20%.
Demand for community testing has also increased by 100% in the last few weeks, he said.
On the roll-out of the vaccination programme, which began yesterday, Mr Reid said the "immediate focus" in the coming days would be on healthcare workers.
Additional reporting by Andrew Lowth