About 25 beds remain closed for a second day at Altnagelvin Hospital in Londonderry due to a vomiting bug and staff shortages.
The Western Health Trust has said there is unlikely to be any change before the weekend.
Staff shortages at the trust have been described by senior management as "worrying".
Speaking to the BBC, the trust's Medical Director Dermot Hughes revealed they are currently 125 nurses short.
"It is an ongoing pressure both in nursing and in medicine. We struggle to recruit to the full amount," he said.
"We have 3,000 nurses and currently are around 125 short.
"We have gone internationally to recruit and we will have a cohort of new nurses in September but there is a problem over the summertime."
The Director of the Royal College of Nursing (RCN) described the system as "falling apart".
Janice Smyth said the recruitment problem could have been avoided if people had listened to warnings from the RCN.
"I think it is a crisis yes and I think we are seeing it in the Western Health Trust first and others to come unless we do something about it.
"If we had done work force planning properly and if people had listened to the warning that the RCN has given this could have been prevented.
"We have been saying for some time that our system is unsustainable and is starting to fall apart."
The Western Trust also said delayed discharges among patients was adding to the problem.
That means, due to a lack of home care packages being available in the community, patients are having to remain unnecessarily in hospital.
At present, no other health trust is reporting being affected by the vomiting bug that has closed beds at Altnagelvin.
Increased infection prevention and control measures have been put in place and all non-urgent routine procedures will be cancelled.