The number of admitted patients waiting for a bed on a Friday has shot up by more than 50% in the past year, latest figures show.
Members of the Irish Nurses and Midwives Organisation counted 608 admitted patients waiting on trolleys in emergency departments and on wards.
An INMO spokesman said it is one of the worst Fridays they have ever seen.
"It sets the scene for the winter," he warned.
The county's public acute hospitals are coming under increased pressure with more flu cases, respiratory viruses and the winter vomiting bug.
The worst-hit hospitals were Cork Unversity Hospital with 57 patients waiting and University Hospital Limerick which had 55.
On the comparable Friday last year, there were 395 admitted patients waiting, according to the INMO's Trolley Watch, so the year on year increase is 54%.
The HSE only counts patients on trolleys in EDs and there were 439 — a 60% increase on last year when there were 275.
Among the patients on trolleys were 209 who had been waiting more than nine hours and 88 who had been waiting more than 24 hours.