There are 532 patients waiting admission to a hospital bed, with Cork University Hospital the worst affected, according to figures from the Irish Nurses and Midwives Organisation.
The INMO said there are 84 patients waiting for a hospital bed at CUH, which is the highest number recorded since the union began collating its Trolleywatch numbers in 2006.
There are 77 patients waiting for a bed at University Hospital Limerick; 40 at University Hospital Galway and 38 at Letterkenny University Hospital.
The INMO figures also show that 11 children are waiting admission to a hospital bed - seven at Children's Health Ireland Crumlin and four at CHI Temple Street.
INMO Industrial Relations Officer Liam Conway said the figures at CUH are "no surprise to those working in the hospital" and said the "discharge rates simply are not keeping up with the admission rates".
He described the situation as "very dangerous" and said "staff can’t wait any longer for the South/Southwest Hospital Group to intervene".
Mr Conway added: "Year in and year out, we see the same problems in CUH at wintertime. Staff feel abandoned because they feel that neither the hospital group nor the HSE are listening to their concerns."
He said "all non-emergency activity" in the hospital should be curtailed and "all private capacity in the region utilised where possible."
"Unless the South/Southwest Hospital Group takes urgent action, we are going to see many more record-breaking days like this in Cork University Hospital," Mr Conway said.
