The threat of losing major reef networks and historic Indigenous rock art forever has led to a legal battle over a major gas mining project extension.

Hearings began on Tuesday for two groups challenging Environment Minister Murray Watt’s decision to grant a 40-year extension of Woodside’s North West Shelf gas hub at Western Australia’s Pilbara region.

The processing plant is one of the largest liquefied natural gas projects in the world, with more than $34 billion invested since it opened in the 1980s.

The Australian Conservation Foundation and Friends of Australian Rock Art claim the project’s extension will heavily contribute to adverse climate change impacts and harm 40,000-year-old rock art.

The groups argue the minister signed off on extending operations until 2070, without knowing the details of the gas project and what pollution it will cause.

Dozens of environmental activists gathered outside the court in Melbourne on Tuesday morning – some dressed as coral reefs and marine species, others in wetsuits and snorkels – to drum up support for the legal challenge.

Governments must stop approving new coal and gas projects as heat records tumble and the climate crisis accelerates, Australian Conservation Foundation chief executive Adam Bandt said.

“You can’t say that you’re trying to put a fire out while you’re pouring petrol on it,” he said outside court.

“If governments don’t do the right thing, then we’ve got to take them to court to get the laws of this country upheld.

“Decisions that get made today are going to have ramifications for generations.”

Lawyers for the Australian Conservation Foundation will argue the minister wrongly considered the economic benefits of an unapproved Browse gas project – a separate Woodside proposal to develop a gas field off the Kimberley coast.

The Northwest Shelf project alone will unleash an estimated four billion tons of climate pollution over its lifetime, ACF general counsel Adam Beeson said.

“That is equivalent to what the entire population of Australia will produce in a decade,” he said.

Senator Watt also failed to consider the physical effects of climate change as an “impact”, the foundation says.

In a submission to the court, lawyers for the minister argued the grounds on which the groups were challenging the decision were invalid and should be dismissed.

Woodside will also weigh in during the hearings to defend the project’s extension, arguing the approval followed a comprehensive and extended assessment carried out by both federal and state regulators in accordance with statutory processes.

Friends of Australian Rock Art said its challenge was launched on top of its ongoing WA Supreme Court action against the North West Shelf’s state approval.

The minister failed to properly take into account the economic and social harms that would result from ongoing damage to the heritage of the Murujuga people.

Co-convener Susan Swain said emissions from the project lead to acid rains that dissolve the 50,000-year-old rock art.

The North West Shelf project extension was referred to the federal regulator in November 2018 and was under assessment for nearly seven years, Woodside has said.

According to the Australian Conservation Foundation, if it goes ahead, by 2070 the North West Shelf Extension will generate around four billion tonnes of greenhouse gas emissions – roughly 10 times Australia’s total annual emissions.