More patients and staff at Dunedin and Wakari hospitals have the symptoms of norovirus. The total number of people affected is more than 100.
The two hospitals have been in lockdown mode since Saturday; three wards are closed on Wednesday morning.
Dunedin hospital says three staff called in sick overnight and two more patients developed vomiting and diahorrea.
Surgery will go ahead on Wednesday on two patients who need urgent treatment and some oupatient services will start again.
The hospital says outpatient services for 2200 people have been cancelled to date.
Health officials believe the norovirus is likely to be affecting the wider community and warn anyone with symptoms to stay home.
Medical Officer of Health John Holmes says norovirus is a non-notifiable disease that is tested for only when two or more cases linked to a common source occur.
Dr Holmes said on Tuesday that the illness, which causes vomiting and diarrhoea, has appeared in rest homes and private hospitals as well.
He said anyone with norovirus symptoms should stay at home for several days to prevent the bug from spreading.