An energy giant has vowed to "vigorously defend" two legal challenges sparked by the controversial extension of Australia's biggest gas project near ancient Aboriginal rock art.

Woodside is set to weigh in to the landmark legal battle over the federal government's approval of the North West Shelf gas hub extension until 2070 in Western Australia.

The first legal challenges to September's commonwealth approval have been launched by conservation groups in a bid to overturn the 40-year extension and protect the nearby World Heritage-listed rock art.

The Australian Conservation Foundation has started Federal Court proceedings in Melbourne to challenge Environment Minister Murray Watt's extension approval of the Pilbara project.

Friends of Australian Rock Art has also begun a Federal Court

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