The number of people waiting for hospital beds reached a record high last night, with 455 patients on A&E trolleys, the Irish Nurses' Organisation (INO) said..
It claimed Cork University Hospital and St Vincent's hospital, Dublin, where more than 60 patients have been struck with the winter-vomiting bug, had the greatest number of patients awaiting admission.
The Health Service Executive (HSE) denied the increase, saying just 363 patients were waiting for admission.
"There are 162 admissions in the east of the country and 201 regionally," a spokesperson said. "Bearing in mind that accident and emergency admission figures are rarely more that 300, today's regional figure indicates a temporary spike in A&E activity outside of Dublin."
Tony Fitzpatrick, INO industrial relations officer, said the situation was getting worse for frontline staff.
"Our members are trying to deliver quality care, but the situation is intolerable.
"There is a big increase in the number of patients waiting for beds, and an increase in the amount of time they are waiting.
"Some people are in A&E for days and returning home despite never getting on a hospital ward. A&E departments are at breaking point."
The situation could worsen with news that the winter-vomiting virus has spread in St Vincent's hospital. Most elective admissions have been deferred.
A statement said the hospital was taking all the necessary precautions to curtail the spread of the virus but 11 wards were affected.
St Vincent's has appealed to the public not to attend the emergency department if only complaining of the effects of the virus. It also asked the public to avoid visiting patients. Visits by children are suspended.
The public has also been asked not to visit St Luke's hospital, Kilkenny, and the Midland Regional Hospital, Portlaoise, as the virus has been detected in them.
Fine Gael health spokesman Dr Liam Twomey TD accused Health Minister Mary Harney of abjectly failing to deal with the overcrowding crisis at A&Es.
"If we needed proof that the A&E crisis is out of control the INO figures are just that.
"This situation is chaotic for the hospital staff struggling with winter-vomiting outbreaks and attempting to give the best care possible to their patients.
"It is hellish for the patients, often elderly, waiting on trolleys in uncomfortable and hazardous conditions.
"And, with MRSA and other bugs proliferating, it is inviting a corresponding escalation of hospital-acquired infections."