The New Zealand Ministry for Primary Industries is talking to quarantine agencies in China about testing methods used to check milk powder and baby formula products from New Zealand.
The Administration of Quality Supervision, Inspection and Quarantine has reportedly rejected some milk powder and formula shipments from New Zealand as being substandard.
State media say the agency rejected 270 tonnes of powders in the 14 months to October, mostly from New Zealand and Australia and mostly baby fourmulas.
Twenty six tonnes of one brand of formula was reportedly rejected for containing insuffient iodine.
MPI has been notified of only one rejection, a three tonne consignment of infant formula because its trace element levels were considered to be inconsistent with the Chinese requirements. But further checks in New Zealand showed it complied.
MPI market assurance director Tim Knox has been in contact with the agency in China to point out differences in testing methods which may explain the different results.
He said New Zealand tests analyse a much larger sample of powders, 150 grams compared with five gram samples overseas.
Mr Knox said analysing larger samples is more accurate for checking trace element levels such as iodine.
Fonterra, says as far as it's aware, none of its products have been rejected. But it is concerned about counterfeiters who use New Zealand's name and reputation to sell substandard product that does not come from New Zealand.