UHG has issued a public advisory, as it deals with a Norovirus outbreak and high numbers of flu cases.
It follows very high attendance over recent days, with almost 600 people presenting at the Emergency Department.
UHG says cases of the winter vomiting bug have led to one ward being closed, while several other areas under investigation.
In addition, it's also treating 29 patients with flu and 13 patients with RSV.
According to the INMO, there are 56 patients on trolleys today, one of the highest figures in the country.
UHG says every available bed is in use, and additional surge areas are also in use, which is impacting on elective procedures.
As a result, the public are advised to expect long waiting times if attending the Emergency Department for non-urgent care.
They're also asked to respect visiting restrictions in place, which limit visits to one person per inpatient per day.
