A warning not to eat chilled oysters harvested from north of Auckland has been issued, as they may be contaminated with a gastro bug.
The Ministry for Primary Industries issued the warning as oysters harvested from the Mahurangi Harbour may be contaminated with norovirus.
Matakana Oysters, Orata Marine, Seafood Harbour and Hutchings and Addison are recalling all oysters harvested from the harbour from mid-January.
MPI is yet to confirm batch numbers and brand names. The products have not been exported, and most are sold in the local area in pottles or on the half shell.
MPI food compliance service group manager Melinda Sando said the amount of affected oysters is likely to be "very small".
"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.