The HSE's Dr Colm Henry says the healthcare system is 'overheated', with some hospitals having to provide intensive care outside of intensive care settings.
It comes as the Cabinet Subcommittee on COVID-19 will meet later to consider what action needs to be taken to tackle escalating cases.
Some 617 people are in hospital with the virus as of Monday morning - with 106 of those in ICU on Sunday night.
While on Friday, Dublin's Mater Hospital announced it was limiting activity to essential services only.
Outpatient appointments and elective surgeries have been curtailed "to essential services until further notice".
The hospital says this is in order to deal with "the impact of the latest wave of COVID-19".
Patients whose appointments are being deferred will be contacted by phone. Unless you receive a telephone call, you should attend as normal.
Dr Henry, chief clinical officer with the HSE, told Newstalk Breakfast a link between COVID cases and harm has not been weakened enough.
"We're worried, the trend in cases is going certainly the wrong way - we're getting used to daily cases now between 3,500/4,000 cases a day.
"And that's gone up 30%/40% only within one week.
"And of course translating through, we know that link between cases and harm has been weakened - but it hasn't been broken.
"So we're still seeing a proportion of those cases become ill and require hospitalisation, and indeed intensive care.
"And even if that link is perhaps twice as weak as it was in January, it still means - for large numbers of cases - that's going to translate through in the coming weeks to people who require hospitalisation."
Dr Henry says while it is "difficult" to put a number on a critical figure of ICU admissions, he believes 150 would be significant.
"This past weekend, we've seen our intensive care units - particularly in the Dublin region - under serious pressure.
"Having to cancel other operations and having to exchange patients between hospitals - and having to provide a form of intensive care outside intensive care settings too.
"What you see is an overheated healthcare system at the moment.
"Intensive cares - yes the numbers if it got to 150, certainly would be very very difficult to see us providing the whole range of care at numbers well below that, I would say.
"But it's not just intensive care units - it's the provision of additional care outside intensive care.
"It's the impact it's having on staff: the staff-related absences related to COVID-19 - either directly through [sic] to illness or otherwise - now 4,000 or more.
"It's the impact of providing care outside intensive care units, the impact on emergency departments.
"We know GPs are feeling a lot of pressure, public health departments under huge pressure out there managing outbreaks.
"And of course our testing and tracing system: a phenomenal 180,000 lab tests in one week.
"So it's an overheated healthcare system right across the board".
