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"No government anywhere in the world has ever removed an area this large from conservation on land or sea," he said. "The process, which was commenced by Tony Abbott in 2013, has now been completed by Malcolm Turnbull and locked in by the Senate."

Michelle Grady, deputy director of the Pew Charitable Trusts, said "these plans do not go far enough to ensure that nature is protected in the longer term - something that is deeply regrettable to witness".

While Parliament had voted to bring 44 large offshore regions into operation as parks for the first time, bringing necessary protections to a number of important reefs, seamounts, canyons and an array of unique and diverse marine plants and animals, the area of highest protection had been slashed, she said.

"It is incredibly worrying to see that the protective zoning included in the original declaration has been cut by half, leaving much of Australia’s marine environment vulnerable to industrial fishing and mining," Ms Grady said.

Of the five motions, the reduced protection for the Coral Sea was the most serious because it would allow long-line fishing from the north to the south, and break its sanctuary link to the adjacent Great Barrier Reef, Mr Burke said on Wednesday.

"It's the cradle of the Great Barrier Reef," Mr Burke said. "The government has been at its most brazen", turning the jewel in the conservation crown "into a national embarrassment".