Opposition Leader Peter Dutton has pledged to approve a gas plant extension until 2070 within 30 days if he wins government – a promise dismissed by the government as a “thought bubble”.

On Wednesday, Dutton declared energy giant Woodside’s 50-year North West Shelf gas expansion in Western Australia was a project of national importance.

He promised to fast-track its approval if the Coalition is victorious at the upcoming federal election.

The Coalition is also vowing to change laws to limit the ability of groups opposing environmental approvals to appeal decisions.

Dutton said he was sending a clear message that a Coalition government would be different and provide a different future for Western Australians.

“I’m seeking a mandate from the Australian people, and in particular from the people of Western Australia, to make sure we can keep mining going and we can keep investments and approval processes flowing,” he said in Perth.

“Because without it, there are no jobs.”

He branded Environment Minister Tanya Plibersek as the “minister for no mining”, accusing her and Prime Minister Anthony Albanese of chasing inner-city Sydney and Melbourne Greens voters.

But Albanese dismissed Dutton’s proposal as just “another thought bubble”.

“It lasts about as long as a bit of a soap bubble that comes up from a bubble bath. It just disappears into the ether,” he said.

“They just come up with these things and they walk away from them, whether it’s referendums, whether it be zonal taxation rates, whether it be the other statements that Peter Dutton makes.”

Albanese said the project had arrived on the federal government’s desk only in the past few weeks and the approvals process was being worked through.

“Do we support the gas sector? Yes, but subject to environmental approvals,” he said.

The Australian Conservation Foundation has lashed the proposal, accusing the Coalition of confusing national interest with the commercial interests of a big fossil fuel company.

“If it gets the green light, Woodside’s North West Shelf expansion would emit billions of tonnes of carbon pollution to 2070, drive demand to open new gas fields and continue the deterioration of ancient First Nations rock art at Murujuga,” nature policy adviser Brendan Sydes said.

Greens environment spokeswoman Sarah Hanson-Young said approving the expansion would cause more destruction, pollution and wildlife extinctions, accusing Dutton of launching a “Trump-like attack” on environmental defenders.

“We all have a stake in the health of our environment and his plan to lock communities out of legal avenues is a threat to our democracy and the health of the planet,” she said.

A Woodside spokesman welcomed Dutton’s commitment to fast-track the project assessment.

“Timely approval of the North West Shelf Extension is critical to ensure this nationally significant asset continues to provide a reliable energy supply to Western Australian businesses and homes,” he said.

Woodside got a 50-year extension to continue operating its offshore gas project from the WA government in December, following a six-year approval process.

But Plibersek has delayed her decision on the controversial Burrup Peninsula plant until March 31.

The Coalition’s announcement comes ahead of Labor’s fourth federal budget on Tuesday. With cost-of-living pressures still front of mind for voters, Albanese signalled more energy relief support.

“We will always look towards what we can do in cost of living measures,” he said.

-AAP