The HSE has issued a public advisory as UHG is under serious pressure.
Yesterday, more than 270 people attended the emergency department.
The HSE notes between the approaching bank holiday weekend and Race Week, there will be higher than usual numbers of people in Galway.
Yesterday alone, 272 people presented at the emergency department, with 55 admitted for treatment.
According to the INMO, there are 72 patients on trolleys at UHG today - the second highest in the country.
The HSE says additional surge beds have been opened, but anyone who attends for non-urgent treatment will experience very long waiting times.
Some elective procedures are being cancelled, with priority given to urgent and time-sensitive cases.
The public are asked to only visit the ED at UHG in genuine emergency - and instead consider out of hours GP services, or the Roscommon Injury Unit.
