Auckland Council is warning the Waitakere Ranges may have to be closed as new figures show a deadly pathogen is quickly spreading through the area's kauri trees.
New council figures show 19 per cent of the native giants are now infected with kauri dieback - up from 8 per cent five years ago.
The disease has spread throughout the park, and in worst-affected areas like Piha, kauri will likely be extinct in five years, Auckland Council's report says.
Within a generation, the species could be gone from the Waitakeres.
Scientists have no cure for the Phytophthora 'taxon Agathis' pathogen but it is believed to be spread by hikers. Trees close to popular tracks such as the Hillary Trail are the most disease-ravaged.
Strict hygiene measures such as cleaning hiking boots are not being followed, the council said.
Councillor Penny Hulse said the report made grim reading and some "very tough decisions" had to be made.
Auckland Council is commissioning an independent review into whether it is feasible to stop public access to the ranges, which currently see more than 800,000 visitors each year.
Tree protection groups are calling for the ranges to be closed as a last-ditch measure to slow the disease's spread.
Forest & Bird called kauri dieback a "national crisis caused by the Ministry for Primary Industry's (MPI's) shambolic failure to manage the biosecurity threat".
Spokesman Nick Beveridge said kauri dieback should not be left up to councils and community groups to manage. He called for urgent increases in funding and more research into the disease.
"MPI management of the Kauri Dieback Programme has been shambolic, and responsibility for the spread of the disease lies with them," he said.
"They have shown sustained incompetence at all levels, wasted time and public money and let the disease that is killing kauri spread on their watch."
Ministry for Primary Industries conservation advisor Erik Van Eyndhoven said those claims were disappointing and he strongly refuted them.
He said a multi-agency approach had been agreed in 2009, and MPI was not responsible for delivering operational work on Department of Conservation- or council-administered land.
Day to day operations in the Waitakeres were Auckland Council's responsibility, he said.
Since 2014, $26.5 million had been allocated to fighting kauri dieback, most of which went to the Department of Conservation.