Otago District Health Board says eight patients and 10 staff have developed symptoms since 5pm on Tuesday.
As a result, a ward was closed on Wednesday morning, taking the total number of ward closures at Dunedin and Wakari hospitals since Saturday to four.
Twenty-two patients are in isolation, and visiting restrictions remain in place at both hospitals. Altogether, more than 120 staff and patients affected by the bug there.
Dunedin Hospital says elective surgery and outpatient services for 2200 people have so far been cancelled.
In Greymouth, Grey Base Hospital is urging anyone who may have norovirus not to visit the hospital.
West Coast District Health Board issued the plea to Greymouth residents after the Kowhai Manor Rest Home and Hospital said six residents have the virus. Access to the facility has been restricted.
The rest home believes it is the only place in Greymouth to be affected, but the health board says it is keen to avoid the bug's spread to Grey Base Hospital.
It says that anyone with signs of the illness, which include vomiting and diarrhoea, should stay at home and not visit the hospital or attend any appointments there for two days.