The average waiting time for patients accessing emergency departments last month was over 11 hours, new figures show.
Mercy University Hospital in Cork recorded an average wait time of 21.6 hours, the highest in the country.
Cork University Hospital was the second highest, where average wait times reached 19.6 hours.
The figures were provided by the HSE to Sinn Féin health spokesperson David Cullinane through written parliamentary questions.
Mr Cullinane said that the figures show "major hospitals across the State remain under severe pressure from emergency department overcrowding".
While hospitals in Cork topped the list, long emergency department waiting times were recorded across the country.
The figures reveal an average of approximately 18 hours in Tallaght University Hospital, 17 hours in St Vincent's University Hospital, 15 hours in University Hospital Limerick, 13 hours in Galway University Hospital and 11 hours in Navan General Hospital.
Altogether, around 35% of ED patients in Ireland were waiting more than 12 hours.
The figures also reveal that over 75s were waiting longer when compared with others.
Mr Cullinane said that emergency departments do not have the capacity to handle patients coming their way.
He called for an expansion in emergency, community, and primary care services.
Mr Cullinane also called for a halt on any plans to "downgrade" emergency services in Navan.
"Limerick has still not recovered from downgrading of smaller hospitals, and Limerick Hospital Group has the longest average wait time of any hospital group at nearly 15 hours.
"It is now the single point of failure in the region with no release valve due to the lack of alternatives", Mr Cullinane said.