People are being urged not to attend the emergency department at University Hospital Limerick unless it is absolutely necessary.
The hospital said it is very busy with a high number of people presenting with a variety of complex illnesses, including Covid-19.
In a statement, UHL said anyone with less urgent complaints should expect long delays in the ED, and to consider other alternatives such as minor injury units, out-of-hours GP or pharmacists.
It added: "We are working to ensure that care is prioritised for the sickest patients, and as part of our escalation plan, additional ward rounds, accelerated discharges and identification of patients for transfer to our Model 2 hospitals are all under way.
"We have also opened surge capacity to manage the extremely high levels of activity."
UHL said its injury units are open seven days a week at Ennis Hospital and Nenagh Hospital (8am to 8pm) at at St John's Hospital from 8am to 7pm.
