Fears four people may have contracted Hepatitis A from imported frozen berries have prompted a warning from the Government.
The Ministry for Primary Industries issued a warning over the potential link today.
"Our investigations to date have not revealed a specific cause, but there is an association with consuming imported frozen berries," director of plants, food and environment Peter Thomson said.
He said there had been four cases thought to be linked to the food.
"Recent outbreaks in other countries also suggest this link," he said.
Earlier this year, a hepatitis scare prompted a mass recall of frozen berries in Australia.
The ministry said it had begun a surveillance program that included extra testing of imported berries.
It said stock previously imported and held by food companies in New Zealand would be checked as well.
Mr Thomson said in the meantime, people could briefly boil any frozen berries if they had concerns.
"Elderly persons and those with chronic liver damage should avoid frozen berries that have not been heat treated," he said.
The ministry said fresh berries or products containing frozen berries had not been implicated in its investigation.
Hepatitis A is a foodborne disease that can spread through food being handled by someone already infected.
Symptoms include fever, skin turning a tinge of yellow, loss of appetite, nausea, vomiting and stomach pains.