Twenty properties around the country are now infected with myrtle rust.

The affected properties are a mix of nurseries, private gardens, retailers or distributors and an orchard, the Ministry for Primary Industries (MPI) said.

Myrtle rust is a significant disease of plant species from the Myrtaceae and has been spreading rapidly around the world in recent years.

At the moment, 16 properties in Taranaki, three in Northland and one in Waikato all have infected plants.

To date, the rust has been found on pōhutukawa, lophomyrtus, eucalyptus and a single instance each of mānuka and Syzgimum smithii. It has not been observed on feijoa as yet.

MPI is receiving unprecedented support from members of the public, with well over 450 reports of suspected symptoms to its 0800 number.

It is working closely with the Department of Conservation DOC in the effort to manage the situation.

People are encouraged to look for signs of myrtle rust, including in the South Island. Many common garden plants are members of the myrtle family and any new growth is susceptible, so people are being asked to carefully examine the underside of new leaves in Lily-Pily (Eugenia), bottlebrush, mānuka, gum, guava and feijoia, especially if they are recently purchased plants from nurseries or ordered online.

Any suspected signs of myrtle rust can be reported to MPI's Exotic Pest and Disease Hotline on 0800 80 99 66.

People should not touch the rust or the plant because the fine wind-borne spores are easily spread on clothes or shoes. Note the location and take photos of the symptoms and the plant.