"We haven't got that much information yet. We've got two areas that we think might be contaminated, Tangiteroria and somewhere in the Hokianga."
The stock on the farms potentially affected at the moment were beef cattle, not dairy cows, he said.
"But that could change by the end of the day."
Cullen said he was particularly concerned as a farmer himself who has recently bought stock.
"We bought some heifers in for this season so we're a bit worried. And that was the first time in years."
A Notice of Direction meant that cattle could not be moved off the farm without a permit, but was not as strict as a Restricted Place Notice (RPN), which restricted movement of all stock and risk goods.
Federated Farmers Northland president John Blackwell said that Northland farmers want an independent inquiry into the disease.
Mycoplasma bovis was confirmed in Waikato just over a week ago. The only other confirmed cases in the North Island were in Hawke's Bay and a farm near Pahiatua.
The disease was first detected in New Zealand in July last year at a farm in South Canterbury.