Opposition Leader Chris Minns, who is seeking to topple the NSW Coalition at this month's election, used a speech today in western Sydney to make his party's position on the tunnel clear.

He said NSW Labor was not convinced that the NSW Government had "properly completed its planning" for the 11-kilometre "unfunded tunnel" from Little Hartley to Blackheath.

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"This could be an $8 to $11 billion tunnel," he told the Future Western Sydney event.

"It has no business case. And it only has $1.1 billion allocated to it in the budget. And let's be clear, that does not buy you an 11km tunnel under the Blue Mountains.

"The remaining $10 billion cannot be found. It's not in the budget - and is completely unfunded. That $1.1 billion is far better spent on local roads across western Sydney and regional NSW."

Mr Minns' declaration of his position on the proposed tunnel was seized upon by Bathurst MP and Deputy Premier Paul Toole, who said the move "sent a clear message to regional NSW that under Labor the building of legacy infrastructure projects would come to a grinding halt".

"Chris Minns is setting a whole new standard for cancel culture - he's already cancelled two Metro [rail] lines critical for western Sydney and now he's cancelling a game-changing highway upgrade that would better connect Sydney with western NSW," Mr Toole said.

"It's becoming clearer by the day that Labor won't build the infrastructure our state needs and that NSW will stall.

"NSW Labor built nothing for 16 years when they were last in office and now they're running on an election platform of doing nothing for the next four."

Minister for Regional Transport and Roads Sam Farraway said the NSW Coalition's "Great Western Highway upgrade will transform travel for the thousands of people who use this road every day".

"Under Labor, it will be scrapped and those thousands of people - and the rest of NSW - will be stuck at a standstill," he said.

Mr Minns said the NSW Coalition would leave behind the largest debt ever handed from one government to another in the history of the state and NSW Labor "will not privatise assets and we will not run up unsustainable debt".

He said NSW Labor will prioritise roads "that people actually need - and which can be delivered by the next government".

The Minns Opposition's decision on the Great Western Highway tunnel is the latest twist in the story of the overall highway upgrade from Lithgow to Katoomba and its ambitious central feature.

While work on the small Medlow Bath section of the highway duplication and another section between Lithgow and Little Hartley is due to start this month, Federal Government funding was delayed last year for the larger east and west sections of the project.

Meanwhile, the central section - the proposed tunnel from Little Hartley to Blackheath - has money committed to it from the current NSW Government but still needs billions of dollars in Federal Government money for it to become a reality.

Federal Infrastructure Minister Catherine King said earlier this year that there was no federal money available for the proposed tunnel.

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