A ward has been closed to new admissions at Arrowe Park Hospital after patients contracted Norovirus - the winter vomiting bug.
The hospital reports an increase in the number of people coming into its Accident and Emergency department with symptoms of the bug.
Now managers are urgently reminding the public the casualty unit is for emergency and life-threatening conditions only.
A hospital spokesman said: "Norovirus is a highly-contagious bug.
"It can be spread very easily both by contact with someone who has the virus but also by contact with surfaces and items they have touched.
"In order to keep our hospital services running as normal as possible, there are some really basic steps to help.
"If you have been sick or had diarrhoea within the last 48 hours then please do not visit A&E unless it is a real emergency."
If you are coming into hospital to visit friends or family over the coming days, you are advised to avoid visiting if you are unwell or if you have been in contact with anyone who has diarrhoea and vomiting. Use hand gels when you enter and leave the hospital.
Nationally, there has been a rise in the number of people being admitted to hospital in an emergency following a "very busy" week for A&E.
Data from NHS England revealed there were 106,230 emergency admissions across England in the week ending February 9, up from 105,053 the week before.
In the same week in 2013, there were 100,834 emergency admissions.
Overall, 418,838 people attended A&E last week.
The NHS missed its target of treating 95% of patients within four hours, instead hitting 94.3%.
The figures cover all centres - major A&Es, smaller minor injury units and NHS urgent care centres.