Plant-killing fungal disease myrtle rust has been found in a new area of the Waikato region, the Ministry for Primary Industries says.

When winter set in slowing the disease's progress, there had been nearly 100 cases of the fungal infection found on plants since April, 64 being in Taranaki, but also in the Bay of Plenty, Northland and King Country.

Now the Ministry for Primary Industries says infections have been found on ramarama trees on two properties in the Otorohanga township - outside the known infection area.

Incident controller Catherine Duthie says the two new properties don't have any connection to those infected in Taranaki, supporting the ministry's theory the disease had blown over in a single wind event, rather than spreading around New Zealand.

"We've been carrying out surveillance for the disease throughout the winter, even though myrtle rust is generally inactive in colder weather and the symptoms are less obvious," Dr Duthie said.

"We had known that a reappearance of obvious myrtle rust symptoms was likely in spring - so while this is disappointing, it's not unexpected."

The properties have been placed under legal restrictions and the infected plants would be destroyed, she said.

Severe infections of myrtle rust can kill plants and in Australia it caused the extinction of several species of significance to Aborigines, as well as hitting commercial crops.

There is no known method for controlling myrtle rust in the wild, other than applying fungicide in very small areas.