Outbreaks of norovirus have hit Auckland's Middlemore hospital and Tauranga Hospital.
About 30 patients in Tauranga have the virus, prompting staff to put four wards under close supervision.
Norovirus causes nausea, abdominal pain, vomiting and diarrhoea.
Bay of Plenty health officials are warning against unnecessary visits to the hospital. Any visitors are advised to carefully wash their hands to avoid spreading the virus.
The Tauranga outbreak follows one at Middlemore Hospital in Auckland, where at least six patients and staff fell ill with the infectious bug late last week.
Two wards at the hospital were put under close monitoring.