The Health Service Executive has said industrial action by nurses was causing significant delays and congestion in hospitals.
Nurses began a work-to-rule this morning in a dispute over pay and conditions.
The HSE is to decide this afternoon on whether to cancel outpatient clinics and planned operations in hospitals because of the nurses' action.
The situation has been monitored since 7am this morning at the National Incident Room in the Phoenix Park in Dublin.
Gerry O'Dwyer of the HSE said it was concerned about the number of patients attending Accident and Emergency departments, and the management of beds.
The executive has appealed to people not to telephone hospitals unless it is absolutely necessary, as calls are putting an extra strain on the system with the refusal of nurses to answer telephones.
There have been no cancellations of elective procedures or outpatient appointments at Cork University Hospital, which is the biggest general hospital outside of Dublin, with 618 beds.
However, CUH General Manager Tony McNamara says the nurses' action will have a serious impact on patient care.
There are 1,300 members of the Irish Nurses Organisation on campus.
Both management and unions were to meet locally today to discuss contingency plans.
Disruptions
Elsewhere, the HSE in the mid-west and west has said it believes the work-to-rule by nurses will cause significant disruption to hospital services today.
A spokesperson in the Limerick region said there had been no specific cancellations as a result of the action, and the situation will be monitored at the region's public hospitals in Limerick, Ennis and Nenagh throughout the day.
However, the HSE has warned that nurses have placed a ban on all clerical, administrative and IT duties and that nursing and midwifery notes will be maintained manually. They have also placed a ban on all telephone work.
The HSE says this will have particular consequences for patients and their families.
The executive claims that the refusal of nurses to use IT-based triage systems in Accident and Emergency departments could hinder bed management, slow down discharge of patients and cause congestion in emergency departments.
It also says the work-to-rule over telephones would pose significant difficulties for relatives inquiring about sick family members.
The HSE claims the welfare of patients who rely on telephone contact with specialist nurses in the areas of oncology, neurology and diabetes will be compromised.
