India's Adani Enterprises Ltd faces a new delay on a planned coal mine in Australia, amid worries that a port expansion to accommodate the project could hurt the World Heritage-listed Great Barrier Reef.

Australian Environment Minister Greg Hunt has extended his review of Adani's A$16.5 billion ($15.5 billion) Carmichael coal and rail project to Aug. 1, a spokesperson for the minister said on Tuesday.

"The date for a decision has been extended to ensure the minister can thoroughly consider the large volume of material associated with this project referral," Hunt's spokesperson said in an email to Reuters.

The project in the untapped Galilee Basin, designed to produce 60 million tonnes a year of thermal coal used in power stations, has been attacked by green groups opposed to both new coal mines and the rail lines and ports needed to ship the coal.

The port that Adani plans to use, Abbot Point, is facing a legal challenge from green groups fighting an expansion that will dredge up 3 million cubic metres of sand to be dumped near the Great Barrier Reef.

The government's move to postpone a decision on the Carmichael project comes just as UNESCO's World Heritage Committee is due to consider a proposal to vote next year on putting the Great Barrier Reef on the "in danger" list.

"Approving [the project] now would have been tantamount to an act of provocation, with UNESCO currently mulling the status of Australia's greatest natural icon," Greenpeace programme head Ben Pearson said in a statement.

The state of Queensland, eager to promote new coal developments to boost the economy, approved the project in May with 190 conditions.