This file illustration photo shows tropical fish swimming near coral reefs. Australian green activists have expressed outrage at a government decision to allow energy giant Shell to drill for gas at a pristine reef that was listed as a World Heritage site just two weeks ago.

Australian green activists expressed outrage at a government decision to allow energy giant Shell to drill for gas at a pristine reef that was listed as a World Heritage site just two weeks ago.

Ningaloo Reef is considered a natural wonder, sprawling some 260 kilometres (155 miles) along Australia's west coast and teeming with hundreds of tropical fish and .

The UN's cultural body UNESCO listed the remote Ningaloo coast as a late last month due to its reef, and white whales.

But environmentalists say it could be under threat after the Australian government green-lighted a proposal from Shell to explore for gas nearby.

"We are very concerned that the Australian government is even allowing the oil and gas sector to operate so close to the World Heritage-listed Ningaloo Reef," WWF's Paul Gamblin told ABC Radio

"It really beggars belief that they aren't requiring a full environmental estimate of Shell's latest drilling proposal."

Gamblin said the Shell operations would run along the side of the reef itself, a "new frontier" for drilling, which has previously been confined to its northern corner.

Shell issued a statement saying it was "mindful of the significant biodiversity and heritage values of the Ningaloo region and we continue to plan our operations accordingly," noting its long safety record in the region.

"The proposed exploration well is targeting gas and would be around 70km from the Ningaloo Reef and 50km from the boundary of the Ningaloo Marine Park and Area," the energy firm said.

Environment Minister Tony Burke said Australia had beefed up its regulatory processes since the Montara oil spill in the Timor Sea two years ago, which saw thousands of barrels of crude spew into west coast waters over 10 weeks.

"Since the Montara incident, the department has adopted a more rigorous process for the assessment of offshore petroleum activities and the approval conditions," Burke told AFP in a statement.

"Shell’s proposal to undertake exploration drilling west of Ningaloo Reef was considered on its merits in accordance with national environment law," he added.

Burke said Australia was "committed to protecting Australia’s unique environment including our oceans" and the Shell approval was consistent with similar projects.