Hastings farmers say the outbreak of the cattle disease Mycoplasma bovis may spread further in the district if it was introduced through live animals from infected areas of the South Island.
It is the first time the disease has been found in the North Island.
The farm, in the Hastings District, is in lockdown.
Other new sites for the disease were on dairy farms in Winton and Ashburton, where more than 5000 cattle were being slaughtered, transported in dedicated stock trucks.
A lot of culled dairy cows were sold today at the Stortford Lodge sales yards in Hastings. A sales yard representative said it was disappointing the Ministry for Primary Industries had not been in touch about the outbreak.
Distance is not a barrier to cattle sales and one farmer said he recently bought 1200 South Island dairy calves from the South Island, which were given rest stops on the journey - a prime opportunity for the spread of the disease which causes serious illness such as udder infections, abortions, pneumonia and arthritis.