The HSE is warning that the number of people in intensive care with COVID-19 may soon exceed the previous peak of 160.
There are currently 1,151 people hospitalised with the virus, another new high number during the pandemic.
It includes 101 people in intensive care - the first time the ICU number has risen above 100 since April.
Meanwhile, around 2,700 healthcare staff are unavailable for work, while there are also 'challenges' in staffing nursing homes in some areas.
The INMO has warned that staffing levels are "in freefall" due to coronavirus-related absences.
The HSE's Chief Operations Officer Anne O'Connor told Newstalk Breakfast that hospitals are coping, but only because non-COVID care has been scaled back.
She said: "When we describe our hospitals as coping, it's important for people to understand that's because they're not doing other things.
"There will be people out there who've had their procedures and appointments cancelled this week, which is very difficult for them.
"We have sites that are very busy - we are very concerned, and certainly the growth coming into our ICUs is inevitable really when you look at the numbers coming in in the first place."
Ms O'Connor said there are positive indicators in the COVID-19 data, such as a reduction in the number of close contacts.
However, she added: "There is a time lag - the big number people see in terms of cases every day, it takes some time for that number to translate into people coming into hospital - and more time again for that to translate into numbers into ICU.
"We're looking at this over the next couple of weeks as still being a very big number. We're working on the basis we will potentially see 2,500 people in hospital - and 300-400 in our ICUs."
She added that those numbers hopefully won't come to pass if people take the right actions and follow the public health guidelines.
