Five wards have closed at Hull Royal Infirmary following an outbreak of Norovirus.
Wards 8, 80, 10, 11 and 120 are closed to new admissions, Hull and East Yorkshire Hospitals NHS Trust said this afternoon.
People who have experienced symptoms - diarrhoea or vomiting - are being asked to stay away, until they have been symptom-free for 48 hours as it is extremely contagious.
The outbreak is adding to the pressures on the hospital, as it is restricting the movement of some patients and cutting capacity for new admissions.
A trust spokesman said it seemed to be a particularly contagious strain: “Unfortunately, bugs like these can spread quickly and easily when you have a number of people in close proximity, such as on a hospital ward.
“Healthy people who suffer from Norovirus or other vomiting bugs are generally able to shake them off within a day or two, but for people who already need hospital care, who may be frail or more vulnerable to infection, catching something like this on top of an existing health problem can be particularly dangerous.”
Norovirus is the commonest cause of outbreaks of gastroenteritis in hospitals. The illness is usually quite mild, lasting around 48 hours.
However people can remain infectious for a further 48 hours after the symptoms have gone away.