The last disease-free koala colony in NSW would be protected in a dedicated national park under a new election promise.
Opposition Leader Luke Foley on Sunday announced the plan to establish Sydney's first koala national park at Smiths Creek Reserve, a sliver of bushland wedged between homes in Campbelltown.
"None of this is rocket science, we know what can be done to save the koala, it's a question of political will," Mr Foley told reporters.
"If we don't act now, the last koalas in metropolitan Sydney will become extinct over the enxt 10 or 20 years."
NSW Labor has already backed a National Parks Association of NSW campaign to turn 175,000 hectares of state forests near Coffs Harbour into the Great Koala National Park.
Chlamydia, a highly infectious bacterial disease that weakens the marsupial and can affect fertility, has wiped out many koalas across the country.
That and other threats including expanding cities, have led koala numbers in NSW to decrease an estimated 26 per cent in the past two decades, the environment department says.
The Berejiklian government has committed to building a koala sanctuary in Pottsville, near Tweed Heads, as part of its $45 million NSW Koala Strategy.
The long-term plan aims to stabilise priority populations and increase koala numbers across the state.
But opposition environment spokeswoman Penny Sharpe said the government's approach didn't stack up.
"They are currently protecting land that hasn't seen a koala on it for over 20 years," Ms Sharpe told reporters.