Northwest NSW locals have vowed to keep fighting against a controversial coal seam gas project while experts and environmentalists have voiced their dismay after it was approved.

The Narrabri coal seam gas project, proposed by oil and gas giant Santos, was on Wednesday granted a phased approval by the NSW Independent Planning Commission subject to 134 conditions.

The decision was viewed with overwhelming concern from some locals vowing to keep fighting against the $3.6 billion project to be built in the Pilliga forest and nearby grazing land.

Narrabri farmer Stuart Murray says the project doesn’t stack up economically or scientifically.

“It’s put a big dent in my trust in the process. I have been fighting this project for years, and truthfully, today, I was hoping for a rest. So now, the fight goes on,” he said in a statement.

Mullaley farmer Robyn King has vowed to not sit back and accept the decision.

“This is the fight of our lives and we can’t afford to give it up,” she said in a statement.

Coonamble stock and station agent David Chadwick described coal seam gas as “mother nature’s melanoma”.

He said it was up to every Australian to stop the project.

Environmental groups and MPs raised concerns about the project’s impacts on koala populations and other threatened species in the Pilliga forest as well as climate change.

The Climate Council says it’s a “dark day” which will send Australia backward.

“Approving this project and developing new gas is fundamentally at odds with protecting Australians from climate change,” climate expert Professor Will Steffen said.

Nature Conservation Council of NSW says the approval gives Santos the green light to “desecrate” the Pilliga forest and endanger koalas.

Greenpeace Australia said the project has “unacceptable” impacts and called on the federal environment minister to reject it.

NSW Greens MP Cate Faehrmann labelled it a “disastrous” decision that will have irreversible impacts on the Pilliga forest and threaten species, farmland and underground water supplies.

“With 850 gas wells planned, along with more roads and pipelines, the Pilliga forest is going to be absolutely decimated,” she said in a statement.

Independent MP Justin Field described it as a “hugely disappointing” decision made amid a climate and extinction crisis that shows the planning system is “broken”.

Energy and climate experts have also warned the project will lock Australia into higher power prices and emissions.

Dr Madeline Taylor from the University of Sydney Law School says it should have been rejected as it risks becoming a stranded asset given the age of gas is in decline.

The Country Women’s Association of NSW says it’s “totally disillusioned” with state planning processes and questioned how a project with 134 conditions can go ahead.

“If a project needs this many conditions, it’s an indication that they need to go back to the drawing board. It doesn’t stack up,” chief executive Danica Leys said.

The state’s peak farming body argues the project will pose an unacceptable risk to water resources, soil and air quality and food production in western NSW.

NSW Farmers president James Jackson says no conditions imposed can make the project acceptable.

The approval has been welcomed by the Australian Workers’ Union which says it could boost jobs and offer more affordable gas.

Natural gas infrastructure company APA Group also welcomed the approval saying it will now continue its development of a new 460-kilometre gas pipeline to connect the natural gas from Narrabri to homes and businesses across NSW.