A record-breaking number of people attended Irish emergency departments last week, according to HSE data.
It comes as officials warned of serious pressure on the health system as it faces a winter surge, with "extraordinarily high" level of attendance at emergency units.
At a briefing on Thursday, HSE chiefs said the surge could see some elective surgeries cancelled.
HSE chief operations officer Anne O'Connor said: "We hope this peak is a temporary and short-lived thing.
"This is a not a flu-driven surge, this is just sick people coming to our emergency departments."
Ms O'Connor said 27,904 patients attended emergency departments last week, with 6,909 admitted.
The pressure comes as the health service continues to treat Covid-19 patients, with nearly 600 people in hospital with the disease on Thursday.
Just over 3,700 patients aged over 75 attended emergency departments in Ireland last week.
"We are seeing a very, very high level of presentation in our older population," Ms O'Connor said.
"They are presenting sicker, frailer. They are being admitted and staying longer."
Health officials said they suspect the current pressure is a delayed winter surge, with people coming forward for treatment later.
HSE staff said the situation has been worsened by the growing number of older people attending hospitals, while Covid-19 outbreaks in nursing homes have prevented discharges.
There are currently more than 260 Covid outbreaks in nursing homes, according to the latest HSE data.
"What this means is our hospitals are full of people with more acute health needs and it takes those beds out of use for other things," Ms O'Connor said.
The worst impacts are being felt in the south and east of the country.
Health officials said additional funding and extra capacity announced over the last two years were "welcome", but pressures remain.
Ms O'Connor said the situation would be "worse" without the extra funding.
Liam Woods, the national director for acute operations in the HSE, said the health system is relying on the core funding, while it is also "consuming" extra resources.
He namechecked Limerick, as well as St James's Hospital in Dublin, as among the locations where elective care is being scaled back.
