Ireland's mortality rate from Covid-19 is set to rise this month, with the chief medical officer warning current transmission levels put "too many people in funeral homes".
Dr Tony Holohan has urged people to step up their efforts against the virus, saying public health chiefs "haven't been as concerned at any point in the pandemic as we are right now".
A Nphet briefing on Monday heard that the number of people in intensive care units could rise to between 200 and 400 by the middle of January if no action is taken.
It came against the backdrop of a record 6,110 new confirmed cases and six further deaths.
Dr Holohan said: "That level of infection just simply puts too many people in hospital and it puts too many people, unfortunately, in funeral homes.
"That's the reality, we simply can't deal with levels of infection like this, as an acceptable level of infection."
He added: "This is a really, really serious situation and one that demands immediate action.
"But we still have an opportunity to, as a country, come together and take action, to turn this around so that we can limit or mitigate the impact of this.
"We're going to see a very significant impact on mortality."
Dr Holohan warned that the provision of non-Covid care in hospitals is now under threat, with non-urgent services to be scaled back from Wednesday.
There are now 3,000 hospital staff who are out of work because of Covid-19, either through infection or as a close contact.
Dr Liam Woods, HSE national director of acute operations, said the absences are affecting the operation of hospitals right across the country.
He said: "That can be clearly very detrimental. The rate of infection, the rate of the virus in the community is fundamentally affecting what's happening in hospitals."
The high levels of transmission are also posing a risk to the planned reopening of schools after the Christmas break.
Dr Holohan said he met with the Taoiseach on Monday to discuss the issue.
While transmission rates in schools remain low, he said, the high level of transmission in the community now presents a risk to their ongoing operation.
The chief medical officer also urged employers to allow people to work from home where possible, saying they have "a duty of care" to their workers.
Anyone experiencing flu-like symptoms is now advised that they are unlikely to have anything other than Covid-19 and must self-isolate.
Dr Holohan said: "If we are individuals who are experiencing symptoms, and if you have symptoms that are flu like symptoms, now you might as well, accept that this is Covid.
"So if you have those symptoms, if you're waiting for a test, if you've been referred by your GP or if you're waiting for the results of a test, you must self isolate.
"That means staying in your bedroom, away from other people in your house, and not coming into contact with other people."