A health boss says an outbreak of sickness and diarrhoea at two East Yorkshire hospitals is one of the worst in the country over the last few years.
Visiting hours are being restricted at Hull Royal Infirmary.
More than 300 staff and patients have been affected by the Noro virus at Hull Royal Infirmary and Castle Hill Hospital in Cottingham.
Medical director Dr David Hepburn said to have so many people affected was a "significant outbreak".
A total of 23 wards at the two hospitals have been closed.
Staff are hoping wards will have re-opened and things returning to normal by the end of the week.
The hospital underwent a thorough cleaning over the weekend and visiting is being limited to two hours a day in a bid to contain the virus.
People are also banned from bringing fruit and flowers and are being asked to wash their hands before and after every visit.