Health chiefs have closed a ward at Royal Albert Edward Infirmary in Wigan after both patients and staff were struck down by diarrhoea and vomiting.
It's believed the symptoms have been caused by Norovirus, which is reportedly 'active' in the local area.
One ward has been stopped from taking new admissions, and precautions have been put in place to prevent the bug from spreading any further.
Hospital bosses are asking people suffering from sickness or diarrhoea to stay away, and have also asked the elderly and very young not to visit.
A spokesman for Wrightington, Wigan and Leigh NHS Foundation Trust said: "WWL can confirm that the Royal Albert Edward Infirmary is experiencing an increased incidence of diarrhoea and vomiting in both patients and staff.
"Symptoms of diarrhoea and vomiting are most likely due to a gastroenteritis virus (Norovirus) which is known to be active in the local Wigan community.
"The Infection Prevention and Control team have recommended that one ward does not take new admissions as specimens obtained from patients have identified the presence of the Norovirus.
"WWL wishes to assure Borough residents that all necessary precautions are in place to help contain the spread of the infection.
"Visitors are asked to not visit if they have any symptoms of diarrhoea and/or vomiting and we would politely request that the elderly or very young do not visit."
