The Ministry for Primary Industries is warning of a potential health risk from imported frozen berries, following four cases of Hepatitis A.
The ministry is now running extra tests on all types of imported frozen berries.
The fruits affected are strawberries, raspberries, blackberries and Boysenberries
It will also test previously imported stock held by food companies.
Ministry spokesman Peter Thomson said recent outbreaks overseas, including one in Australia earlier this year, suggested the link.
He said anyone concerned about the safety of their frozen berries should briefly boil them before eating.
"Elderly persons and those with chronic liver damage should avoid frozen berries that have not been heat treated," he said.
People concerned about a potential risk to health should seek advice from a medical practitioner or call the Ministry of Health Healthline (0800 611 116)
Concerned about the safety of food products should be directed to the MPI consumer helpline (0800 008 333).