All citrus produced in Australia's Northern Territory has been blocked from leaving the state after a disease, citrus canker, was detected there.
Citrus canker is spread by wind and rain, and can cause infected trees to suffer from low vigour and a reduction in fruit quality and quantity.
The ABC reported that plants sold from a nursery in Darwin and another in Palmerston were believed to be infected with the contagious disease.
Australia's Department of Agriculture said the vast majority of the country's citrus production areas were geographically isolated from where the disease had been found in Darwin.
"The detection was made in a peri-urban area that is more than 2500km away from key citrus producing areas in South Australia, Victoria and Queensland," it said.
The department said to manage any potential risks to Australia's industries and trade, emergency biosecurity measures have been activated immediately and further planning and traceability work is under way.