Farmers are stunned the cattle disease mycoplasma bovis has spread to Hawke's Bay, a Hastings dairy farmer says.
A property near Hastings and three in Southland have been confirmed as infected and another, near Ashburton, is a suspected case.
Since the disease was first spotted, in July, 12 properties have been infected.
"Tracing is a complex exercise and we did expect we would find other [farms]" - Ministry for Primary Industries director of response Geoff Gwyn
All the infected farms are linked to the Van Leeuwen Dairy Group at the centre of the outbreak and the Ministry for Primary Industries (MPI) has already culled more than 3000 cattle to try to stop the disease spreading.
Hastings District dairy farmer and rural community board member Nick Dawson said news of the spread to Hawke's Bay was a big blow to his community.
"We're all a bit shocked and stunned that it's got to the North Island.
"We felt pretty safe up here but in hindsight it was inevitable. We're one big country and we can't close the barrier between the North and South Island."
He farmers would be devastated if cows had to be killed.
"In my situation we've got a dairy herd with 21 years of breeding, we've got kids school calves in that herd ... we've had the same herd since sharemilking days so it's quite personal.
"I'd be devastated if we had to kill my herd, they're almost part of your family and they've served you well for years and years ... to suddenly have to kill them would be heartbreaking."
MPI said it would re-evaluate its culling plan once it had completed the cull at the seven Van Leeuwen Dairy Group Farms.
Mr Dawson said he was losing confidence the ministry can control the disease. "The horse might have bolted a bit, but I'm sure they're doing everything they can in their powers to contain it."
'Make your farm a fortress'
Federated Farmers president Katie Milne said the latest spread was frustrating and gutting for farmers, but the link to the Van Leeuwen Dairy Group gave her hope.
"It does all trace back to the original farm ... so it is technically still semi contained," she said.
"We still have options to make sure we can move through to get rid of it."
Ms Milne said farmers should take their own precautions.
"It's putting up a temporary fence, or a permanent one if they get around to it, even a reel around their property so there is no nose-to-nose contact with other people's animals.
"Make your farm a fortress is what the aim is now."
Farmers should also put in place their own biosecurity measures such as washing boots of people coming and going on farms, she said.
Agriculture Minister Damien O'Connor said the ministry was doing its best and it was hard to know what else could be done be done to contain the disease.
He wants a daily update on testing results from MPI.
"I want to know on a daily basis what progress is being made in terms of further identification of properties.
"We will be looking to try and contain, within all existing properties identified, all animal movements."
When asked if he thinks this disease is contained, Mr O'Connor said it's hard to know at this stage and he is optimistic, but also realistic.
"Every extra farm that is identified is a big challenge, and any possible animal movements in or out of these properties can contribute to further spread."
MPI is holding a public meeting in Hastings on 20 December.