"Our main concern, however, is that people may have frozen the oysters and still have them in their freezer. It is very important that they are discarded."
There is also a halt on all oyster harvesting from Mahurangi Harbour.
Sando said MPI were alerted to the risk of the gastro bug after 11 people became ill after eating oysters from the area.
"Samples of the oysters were tested by ESR and norovirus was found. The type of virus is the same as that found in the affected people."
Norovirus gastroenteritis generally presents with vomiting followed by diarrhoea. The ministry advises people who believe they have eaten affected oysters to see their doctor if symptoms are severe or persistent, or if they are unable to keep hydrated.
Information is also available through the Ministry of Health's Helpline at 0800 611 116.
Sando said the problem appears to be limited to a small area of the harbour around Dyers Creek.
"It is likely to be the result of a localised contamination - for example discharge from a boat or a leaking septic tank."
MPI is continuing to investigate.