About two dozen protesters carrying anti-Labor and climate action signs lay on the floor in the West Perth building for about 15 minutes on Friday singing "climate justice now".
Former WA Senator Jo Vallentine was arrested and then released at the scene after police ordered the group to vacate the ground floor at the 14-storey building as bemused office workers looked on.
Outside the building, Ms Vallentine told the group greenhouse gas emissions from Woodside's North West Shelf Project would contribute to global warming and "we want this project stopped".
"How dare Roger Cook boast about having got in touch with the prime minister to put the climate legislation off the agenda," she said before police took her into custody.
"So much is at stake - the Scott Reef, the Browse Basin, the gas they want to frack in the Kimberley and put another huge pipeline down to the Burrup (Peninsula)."
The action started outside Woodside Energy's headquarters in the Perth central business district, where about 150 protesters gathered to vent their anger after the WA government approved the project's management environmental plan on Thursday.
Anti-Woodside climate activists occupied the lobby of WA Premier Roger Cook's office in Perth. (Aaron Bunch/AAP PHOTOS)
Woodside described it as a "critical step" in the approvals process following six years of assessments and more than 750 appeals against it.
It also triggers the federal environmental approvals process, which was paused while appeals were being considered.
Mr Cook said the North West Shelf Project extension was needed to provide gas while the state transitioned to renewable energy generation.
"We all look towards a clean energy future, and that's something that we are marching deliberately on, and in fact, are leading the country," he said.
"We are the only state in Australia that will be out of coal by 2030."
The Chamber of Minerals and Energy WA urged Federal Environment Minister Tanya Plibersek to quickly complete the federal assessment and "provide some much-needed certainty for the future of the North West Shelf".
"This a vital project for WA's ongoing prosperity, as well as energy security both here at home and abroad," chief executive Rebecca Tomkinson said.
The Woodside project, in the remote northwest of the nation, was previously given WA environmental approval in 2000 to operate for 30-plus years.
Under the new approval, Woodside agreed to a range of environmental management measures.
The North West Shelf Project includes the Karratha Gas Plant. (Rebecca Le May/AAP PHOTOS)
These included a significant reduction in air emissions and greenhouse gas emissions management action to reduce emissions over time.
The North West Shelf Project is one of the largest liquefied natural gas (LNG) projects in the world and includes the Karratha Gas Plant, about 1500km north of Perth, and three offshore platforms.
It started operating in 1984 and has supplied more than 6000 petajoules of domestic gas for homes and industry, which is enough power for every home in Perth for about 175 years.
Ms Vallentine was issued with an infringement notice, police said.
