Cattle disease Mycoplasma Bovis has been found in the North Island for the first time.
The disease has been detected in Hastings, on one of four new properties that have tested positive.
The other new sites were in Winton and Ashburton, with early indications suggesting the infected properties had links to the Van Leeuwen Dairy Group. The new sites brought the national total to 12.
Already 5000 cattle were being slaughtered but that number was set to rise with the latest positive tests.
The disease could cause udder infections, abortions, pneumonia and arthritis.
Geoff Gwyn from the Ministry of Primary Industries said the affected farms were quarantined.
"The Hastings and Winton properties are now under a Restricted Place Notice under the Biosecurity Act. This effectively places them in quarantine lockdown - restricting the movement of animals and other risk goods on and off the farm.
"The suspect property is under voluntary movement controls until their status is confirmed. MPI is working closely with them."
Gwyn said the Ministry had not decided what would happen next.
"We're still analysing what this means for the wider response. We're dealing with a lot of uncertainty.
"Our investigators are building a picture of stock movements onto and off these farms so we will not be making hasty decisions on next steps."
Listen: Damien O'Connor speaking last month on Mycoplasma bovis
Agriculture and Biosecurity Minister Damien O'Connor said he would meet with officials to discuss the next steps in dealing with the outbreak.
"I understand this is tough for farmers, people working on these properties and people in these close-knit communities, but everyone is working hard to find solutions.''
The Hastings and Ashburton properties were identified through MPI's tracing programme and the Winton property was identified through the industry milk testing programme.
All of the movements were prior to July 21, when the disease was first detected and notified to MPI.
"I know an obvious question people will have is 'Why has it taken this long to find these properties?'," Gwyn said.
"The answer to that lies with the nature of this particular bacteria.
"It is a tricky thing to find and often hides within an animal, lying dormant and not revealing itself for weeks or months. Some cattle may be infected and never show signs of the disease.
"This is why we test multiple times using multiple kinds of tests. Sometimes to confirm the disease we have to test organ tissue from animals at slaughter as was the case in Hastings."
Gwyn said the Ministry was continuing its policy of not naming farms where the disease was found if the owners did not want their properties identified.
Good biosecurity and accurate tracing of animal movement is not an option in today's world, it's an imperative, Federated Farmers president Katie Milne said.
"Don't rely on others to protect your patch, protect it yourself. In the end, we are all biosecurity officers with a role to play.
Close and repeated contact with an infected animal is still regarded as the most likely way Mycoplasma bovis is spread.
"Think about your own actions too. If you're visiting a neighbour, clean your boots and any gear you might bring," Milne said.