Several hospitals in Dublin have curtailed activities to essential services only due to extreme pressure.
They include the Mater Hospital which is limiting activity to essential services only from this evening.
In a statement, it said that "outpatient appointments and elective surgeries will be curtailed to essential services until further notice.
"The Mater regrets the impact that this will have on our patients but these new arrangements are necessary in order to deal with the impact of the latest wave of Covid-19.
"Patients whose appointments are being deferred will be contacted by phone. Unless you receive a telephone call, please attend your appointment as normal.
The Mater Emergency Department is also extremely busy with high numbers attending.
People are being advised to seek help from their GP where possible or local injury clinic unless they think they require hospital care.
Services curtailed at three children's hospitals
Children's Health Ireland (CHI) at Crumlin, Tallaght, and Temple Street have announced the cancellation of some non-urgent elective in-patient and day case procedures from 15 to 19 November.
They said this was due to extremely high numbers of attendances at emergency departments and the urgent care centre at Connolly Hospital in Blanchardstown.
They added that if anyone is scheduled for an in-patient or day case admission during this time, the hospital's admission team will contact them directly prior to their scheduled date.
In a statement, the hospitals confirmed that all out-patient appointments will proceed as scheduled.
Around 40% of in-patients across CHI hospitals have Respiratory Syncytial Virus (RSV) - a common respiratory virus that usually causes mild, cold-like symptoms - while many others have the winter vomiting bug or other viral illnesses.
CHI said that cancelling elective procedures is necessary to provide safe care for patients needing urgent or essential treatment and for staff to manage.
Chief Executive Eilísh Hardiman said: "All of our hospitals - CHI at Crumlin, Temple Street, Tallaght and the Urgent Care Centre at Connolly Hospital - continue to experience extreme pressures on services and staff.
"We fully appreciate cancelling any activity will impact our patients and families and cause distress, especially for those who have waited a long time for appointments - for that we are sorry.
"We need to ensure we can continue to deliver safe care.
"We are reviewing the situation daily and we hope to restore non-urgent services as soon as possible.
"We are working with the HSE on investment to improve access to care for patients on waiting lists."
Dr Ciara Martin, Clinical Director at CHI, said: "We would like to reassure parents and families that our EDs and Urgent Care Centre are open" but warned that people attending these facilities "will likely experience delays".
"If your child is seriously ill or you are worried that their life may be at risk, please attend your nearest ED and we will assess and treat your child as a priority.
"Please consider community services such as your GP or pharmacy if suitable, before you attend one of our hospitals.
"Our staff are working hard to manage this busy period and we are grateful for their commitment to safe patient care," Dr Martin added.