The Mater and Beaumont hospitals closed their accident and emergency rooms for three hours last night due to overcrowding.
The move saw the north side of Dublin left without emergency cover.
People in the eastern region have been urged to only attend the accident and emergency unit of Dublin's main hospitals if "absolutely necessary" after Monday saw over 100 patients on trolleys in A&E units across five city hospitals.
According to the Irish Nurses' Organisation (INO) there were 33 patients on trolleys awaiting beds in the Mater yesterday; 17 on trolleys in Beaumont; 19 on trolleys in St James's; 27 on trolleys in Tallaght hospital; and a further eight on trolleys at James Connolly Memorial Hospital in Blanchardstown.
The INO has called for meetings with hospital managers to discuss ways of opening the 200 beds closed by the hospitals earlier this year due to funding difficulties.