Long waiting times and overcrowding are to be expected in hospitals during "this difficult winter", the Irish Nurses and Midwives Organisation has warned, with 612 admitted patients waiting for a hospital bed this morning.

It follows a statement by University Hospital Limerick over the weekend, in which the hospital advised people not to attend its emergency department unless absolutely necessary due to high volumes of patients presenting.

Similar statements have been issued by St James's Hospital and Tallaght University Hospital in Dublin in recent weeks.

According to the INMO, there were 509 admitted patients in emergency departments waiting for a bed, while 103 are in wards elsewhere.

The hospital worst affected is University Hospital Limerick, where there are 89 people waiting for a bed, with 71 waiting at Cork University Hospital at 43 at Sligo University Hospital.

The INMO said there were 15 patients waiting for a hospital bed at Children's Health Ireland Crumlin and 13 waiting at CHI Temple Street.

Speaking on RTÉ's Morning Ireland, INMO General Secretary Phil Ní Sheaghdha said hospitals are dealing with a predictable winter surge, adding, "we have very poor turnaround in our hospitals, we've had overcrowded hospitals since very early on in the summer this year.

"I think the HSE is very aware, as is the Department of Health, and the winter plan confirms, that this winter is going to be worse than any other and that's the planning that’s now in place".

Ms Ní Sheaghdha said the INMO is calling for earlier planning and realistic measures "to make sure we can discharge people from hospital."

She said that currently there are more than 650 people in hospital who do not need to be there, but due to a lack of community beds there is nowhere for them to go and "this is something that happens every year".

Ms Ní Sheaghdha said there are two main issues facing the hospital system, firstly that out-of-hours GP services need to be increased and that attention must be given to the number of referrals to EDs by those services.

She said her members are reporting an increase in referrals and not all of these people need to attend emergency departments.

Secondly, she said, there is an increase in resignations that must be addressed, saying "these departments are becoming really difficult to work in and we're getting increasingly worried about the number of resignations among nurses particularly".

Ms Ní Sheaghdha said this winter is going to be very difficult, and patients attending must know how long their wait is going to be.

"Attending these hospitals right across the country is going to mean you’re going be waiting for very long periods of time to be seen and then you’re also going to have a wait on a trolley," she said.