A disease which has killed thousands of kauri trees in the past 10 years has spread to the Coromandel, and part of the Whangapoua forest is closed to try to contain it.
The dieback disease, which kills nearly all infected kauri, has been found in Northland, the Waitakere Ranges and on Great Barrier Island.
It is caused by a microscopic, fungus-like organism which infects the roots and damages the tissues which carry water within the tree.
Primary Industries Minister Nathan Guy said its spread to the Coromandel Peninsula was a major blow to conservation efforts.
Conservation Minister Nick Smith said about 320ha in the Whangapoua forest, just north of Whitianga, was infected.
"We've got positive tests on two trees. We have helicopters there testing the wider forest," Dr Smith said.
"The tests have a turnaround period of three or four weeks. It's going to take about six weeks for us to get a good appreciation of how serious this infestation is."
Dr Smith said the research programme to save kauri was up for review in June, and a plan to ramp up the work would be urgently brought forward.
But Forest and Bird advocacy manager Kevin Hackwell said the organisation was not surprised the disease had spread.
"The Government and the local council response to this disease has not been adequate, and if there'd been a more effective response to its presence in places like Auckland, we may not have seen it spread to places like the Coromandel."
Having stations with disinfectant and shoe brushes were vital but not available everywhere in Auckland forests, he said.
Labour Party associate spokesperson for the environment Phil Twyford said groups trying to stop the spread of the disease had been working with limited resources.
"Unless we properly fund the scientific research so that we can better understand the disease and stop the spread of it, then under our watch our generation will be responsible for this iconic New Zealand species becoming endangered and, possibly, extinct."
Researchers urgently needed to secure funding, which would run out in June, Mr Twyford said.