Doctors are warning that more than 1,000 people will be forced to use hospital trolleys this winter due to shortages.
The Irish Medical Organisation said a lack of emergency department resources, beds and recruitment will combine to create what it describes as a "perfect storm" in hospitals over the coming months.
The IMO said it will result in "already stretched hospitals facing another chaotic winter."
IMO President Dr Peadar Gilligan said it will lead to "over 1,000 people being left on trolleys and a severely hampered health service."
Trolley numbers reached a record on 12 March, when 714 people were lying on trolleys waiting for admission to a hospital bed.
The IMO is calling for a strategic plan to be put in place to address the overcrowding issue.
The organisation wants the Government to undertake a sustained recruitment campaign to fill existing vacancies and improve services and for a major investment in acute beds.
It says "patients being cared for in dangerously overcrowded Emergency Departments is a function of an acute hospital system working beyond its available capacity.
"The capacity constraints include nearly 500 unfilled consultant posts and 2,650 less beds than we currently require in Irish hospitals and a need for over 1000 additional General Practitioners."
The IMO also say a widespread investment in general practice and primary care would help to ease the situation.
The warning comes as the latest figures from the Irish Nurses and Midwives Organisation show that there are 403 people on hospital trolleys today waiting for beds.
University Hospital Limerick is the worst affected, with 55 people awaiting admission.
The Department of Health said it is working closely with the HSE to "ensure the most effective response" to the winter challenges and increasing capacity is a priority for the Government.
In a statement, the department said: "Over the past 12 months, an additional 240 beds have been opened and a further 79 additional beds are planned for Quarter 4 2018 and early 2019."
It adds that "a further €10 million will be invested next year to enable additional beds to be opened to alleviate pressure on Emergency Departments for Winter 2019/20 and the years ahead, on foot of the recommendations in the Health Service Capacity Review."
The department also said that "€10m in funding has been allocated in 2018, to enable hospitals to get patients home, where appropriate, before the end of the year, with a focus on supporting patients in the over 75 age group."
