MORE New Zealand dairy products exported to China have been banned after high nitrate levels were detected, heightening concerns over quality control in the world's largest dairy exporter.

The latest scare comes just weeks after 38 tonnes of dairy products from Fonterra were found to be contaminated with a botulism-causing bacteria. This sparked a recall of infant formula products, sports drinks and other products in China, New Zealand and other Asia Pacific nations.

New Zealand's agricultural regulator said it has revoked export certificates for four China-bound consignments of lactoferrin manufactured by Westland Milk Products after higher-than-acceptable nitrate levels were found by tests in China, Reuters reports.

Two of the four consignments, amounting to 390 kilogrammes of affected product, had been shipped to China but not sold to consumers, said New Zealand's Ministry of Primary Industries (MPI).

"Any food safety risk to Chinese consumers is negligible because the quantities of lactoferrin used in consumer products was very small, meaning the nitrate levels in those products would easily be within acceptable levels," said the acting MPI director-general Scott Gallacher.