A controversial India-backed project to develop a huge coal mine near Australia's Great Barrier Reef was Tuesday one step closer to fruition after Queensland state authorities gave it environmental approval.

Adani Enterprises' Carmichael coal mine, set to be one of the world's biggest, has faced numerous hurdles. The need for state and federal consent -- along with legal challenges by conservationists -- has stretched the approvals process to five years.

But Adani was boosted by the Queensland approval -- just over three months after the federal government gave the green light to the Aus$16.5 billion (US$12.1 billion) project in Galilee Basin, while imposing 36 strict environmental conditions.

Queensland's Department of Environment and Heritage Protection said its own approval came with some 140 conditions, including nine focused on the endangered black-throated finch.

It said in a statement it was confident the "strict" conditions "will ensure this mine will not pose an unacceptable risk to the environment and any potential impacts will be closely monitored".

No further details were released by the state government. AFP has sought comment from Adani.

Adani has several other hurdles to overcome in the shape of two legal challenges.

One case was brought by the Wangan and Jagalingou Traditional Owners' Council, an Aboriginal group, on the basis that Adani did not have their consent to build the proposed mine. It is currently in the Federal Court in Brisbane.

The Australian Conservation Foundation is challenging the federal government's approval in another Federal Court case.

Conservationists have argued the mega-mine would threaten the Great Barrier Reef, the world's biggest coral reef ecosystem.

The reef is also threatened by climate change, as well as farming run-off, development and the coral-eating crown-of-thorns starfish.

"With the global coal market plummeting and countries like China, the US and even Vietnam phasing out new coal mines, the Queensland government should be creating a transition plan for coal workers, not backing a dead-end project like Carmichael," Greenpeace said in a statement Tuesday.

A controversial port expansion at Abbot Point in Queensland to support mining projects such as Adani's was approved by the federal government in December, despite fears it too could threaten the reef.

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