Patients have been urged by hospitals, health boards and doctors to stay away from accident and emergency departments this afternoon if at all possible.
The advice has been issued following the decision by A&E nurses at over 30 acute hospitals to take industrial action.
The Health Board's executive has urged patients to visit their GP rather than an A&E unit if they are ill. However, they emphasise that emergencies will still be catered for by casualty departments.
The major Dublin hospitals also issued a statement last night requesting the public to avoid attending A&E "where at all possible".
Those who ignore this advice, as well as those who are referred to A&E by their GPs, can expect even longer delays than normal.
Last night the chairman of the Irish Patients' Association, Mr Stephen McMahon, said he was seriously worried about the impact the strike would have on patient care.
"With respect to all parties, this is a case where patients are used as pawns," he said.
He said he understood the concerns of A&E nurses but did not agree with their tactics. "The justifiable cries of frustration from nurses and healthcare workers is nothing compared to the frustration of patients with the system," he added.
Mr McMahon said that while nurses would provide cover in "life-threatening situations", there was "always a risk patients would be put in danger in situations like this".
The President of the Irish Association of Emergency Medicine, Dr Coleman O'Leary, who is an A&E consultant at Limerick Regional Hospital, said the action could mean doctors would be unable to deliver a prompt service for patients.
"It's only the most seriously ill patients that will be seen at all. If we have the same number of patients attending today as we had yesterday then there will be very significant delays," he said.
"Everything is going to be on slow slow burn so it's going to be pretty miserable."
He said while he understood why nurses were taking the action, it would leave hospitals "in the soup today" and they would have "to fly by the seat of their pants".
Mr Donal Duffy, assistant secretary general of the Irish Hospital Consultants' Association, said that even in emergencies patients could not be guaranteed the same level of service as normal during the action, particularly if a number of emergencies occurred at the same time.