Auckland's Middlemore Hospital is on alert after an outbreak of the stomach bug norovirus.
More than one ward has been affected by the virus, the hospital said, with staff and patients also becoming sick.
Viral gastroenteritis, or norovirus, is a stomach bug which causes nausea, cramps, diarrhoea and vomiting.
Several people have been admitted to Middlemore with the illness in the last few days, it said, with some patients transferring the bug to other patients and staff.
"As of today, there are 11 patients and three staff affected," the hospital said in a statement.