There were 606 people on trolleys in emergency departments or on wards waiting for a bed on Monday morning, according to figures from the Irish Nurses and Midwives Organisation (INMO).
This is the highest number of patients on trolleys since March 2018, according to the organisation.
It said there were 439 patients waiting in the emergency departments while 167 were in wards elsewhere in hospitals.
The figures include 13 children at Our Lady's Children's Hospital in Crumlin and Temple Street Children's University Hospital.
There were no children on trolleys at the National Children's Hospital in Tallaght, according to the figures.
University Hospital Limerick (59) had the largest number of patients waiting on trolleys in the emergency department or on wards waiting for a bed, followed by South Tipperary General Hospital (50) and Cork University Hospital (48).
Letterkenny University Hospital (40), Sligo University Hospital (33) and the Midland Regional Hospital in Mullingar (29) were also badly affected.
In Dublin, the largest number waiting for a bed was 27 at Beaumont Hospital and St Vincent's University Hospital, followed by the Mater (23) and Connolly Hospital, Blanchardstown (21).
Minister for Health Simon Harris acknowledged the trolley numbers were "very high" on Monday.
“The surge was always going to come and we have seen a surge in relation to attendances in the health service, in particular in recent days,” he said.
“Our hospitals are extremely busy, we’ve taken a decision to extend the focus period . . . As part of the winter plan we had a specific focus period with additional resources and additional structure in place. We’ve decided to extend that for the next fortnight.
“My advice to the public remains the same: please keep the emergency departments for emergencies If you do find yourself with a condition, check out things like undertheweather.ie in terms of how you can best manage your own condition at home perhaps rather than spreading infection.
“I want to assure people that everything that can possibly be done is indeed being done.”