A GM-positive test result of a maize consignment is being investigated by the Ministry of Agriculture and Forestry (MAF).
The maize consignment, stored in the upper North Island, was tested as part of normal quality assurance processes and has been isolated while further investigations are completed, the ministry said.
Thisincludes sending independent samples to an overseas laboratory, and results may take three weeks.
MAF eradication programmes manager Ian Gear said the investigation was still in its early stages, and there was little that could be said until those results were available.
He said: "The investigation relates to a consignment of 13,500 tonnes of maize held at locations in the upper North Island. The problem we have is that the sample comes from mixed seed lines and multiple growers.
"We have to take all positive samples seriously, and tracing those seed lines and growers is a priority."
Mr Gear said the maize was destined for manufacture into food products, and thus rendered non-viable.
The next maize crop is due to be planted in October or November, and the nature of the New Zealand farming industry meant it was very unlikely that farmers had held any of this year's crop to plant next season, MAF said.
Maize is unable to reproduce itself.
"We are mindful of the timing of this, but for MAF, this is business as usual. This is the sixth occurrence of this type in the last three years," Mr Gear added.
Biosecurity Minister Jim Sutton said: "We have had several of these scares in the past few years, and officials are dealing with this one in the same way as they have dealt with the others. It's very much business as usual."
