Ambulances were being diverted from the Accident and Emergency department at the Midlands Regional Hospital in Mullingar this evening amid what nurses' representatives called "unsafe" levels of overcrowding.
The HSE however insisted that the department remained open for patients who arrived for treatment.
"The Midland Regional Hospital at Mullingar is currently experiencing a significantly busy period in its A&E, as a result the ambulance service have been asked to re-direct patients to the nearest A&E, for the moment," the HSE said in a statement.
"The A&E will remain open to the general public."
"Ambulances have been asked to divert patients to other available A&E departments in the Midlands," said HSE spokesperson Dympna Bracken, insisting the measure was a temporary one taken to alleviate pressure on the Mullingar A&E during a busy period.
A statement issued earlier in the day by the Irish Nurses' Organisation had said 22 patients were waiting to be admitted to the department, with no trolleys available for new patients coming in.
"Mullingar A&E has seen an 800% increase in the number of patients waiting on trolleys in November 2009 compared to figures for November 2007," the statement said, attributing the increase to the closure of beds in the hospital.
"The A&E Department in Mullingar cannot cope with this level of overcrowding, it is unsafe and unmanageable," said Lorraine Monaghan, INO Industrial Relations Officer.
"This situation will inevitably worsen as we enter into the depths of winter unless management take immediate action."