Overcrowding at Cork University Hospital (CUH) hit record levels on Friday, when 73 patients were counted waiting on trolleys and in wards for admission to a bed.
The figure matches the previous high recorded at CUH in April 2018.
The Irish Nurses and Midwives Organisation (INMO) said the majority of patients without beds were over the age of 75.
"This is a crisis situation. Our members on the frontline are describing the situation as 'horrendous' for both staff and patients," said Liam Conway, INMO industrial relations officer.
He called on the hospital to pause non-emergency admissions, cance elective surgery and source extra bed capacity from the public and private sectors until the situation stabilises.
Mr Conway claimed there had been more than 50 nursing vacancies in CUH for several months “due to the HSE’s cost-cutting ‘go-slow’ recruitment policy”. “After much lobbying, we got the HSE to approve recruitment for the posts on December 20th - far too late to make a difference this winter.”
Overall the INMO said 620 patients deemed to require admission to hospitals were waiting on trolleys in emergency departments and on wards for beds across the State on Friday.
The total included 57 patients at University Hospital Limerick, where the HSE insists a new 60-bed block will open in the last quarter of this year. The highest number of instances of patients waiting for a bed last year, 13,941, was recorded in Limerick.
Minister for Health Simon Harris said he was delivering extra hospital bed capacity for the mid-west, adding that 15 beds had been re-opened at St John’s Hospital Limerick in mid-December as part of the HSE winter plan.
However, UL Hospital Group later clarified that the St John’s beds would not acatually re-open until later this month.
Separately, the Mater Hospital in Dublin urged members of the public to visit only when absolutely necessary. The Mater said it was experiencing high levels of patients admitted with influenza. It said children under the age of 12 were not permitted to visit the hospital. There were 23 patients at the Mater Hospital who required admission waiting on trolleys in the emergency department on Friday, the INMO said.
The South/ South West Hospital Group,meanwhile, urged the public to help prevent the spread of flu by avoiding hospitals, congested emergency departments and contacting GP surgeries by phone, so as not to infect others who may be very unwell already.
Dr Paul Gallagher, consultant geriatrician at CUH, said mild illnesses such as colds, sore throats and coughs were usually viral, self-limiting illnesses and could be treated at home with fluids, over-the-counter painkillers and rest.
"Antibiotics will not work on a viral infection, including flu. Get plenty of rest, drink lots of fluids and take paracetamol or ibuprofen for temperatures, aches and pains," he said. "You can visit hse.ie/winter or undertheweather.ie for useful advice and self-care tips for treating mild viral illnesses".
Dr Gallagher said it was not too late to get the flu vaccine, which he said was free of charge for people in at risk groups.
This included everyone aged 65 years and over, pregnant women and people aged over six months with a long-term illness requiring regular medical follow-up such as chronic lung disease, chronic heart disease, diabetes, cancer or those with lower immunity due to disease or treatment.