Environment Minister Greg Hunt said the project could go ahead, but only under strict conditions aimed at protecting the reef marine park from the 1.1 million cubic metres of sludge that will be dredged to create the port.

All sludge dug up during dredging would have to be disposed of on land rather than at sea, as was originally planned.

The dredge-dumping rules and water-quality guarantees included in the conditions are designed partly to allay concerns raised by the United Nations World Heritage Committee, which after wavering decided in July not to list the reef as an “in danger” site. It remains on UNESCO’s watch list.

The approved expansion will ease coal exports from proposed mining projects in the Galilee Basin, such as Adani’s $12 billion Carmichael mine, which is Australia’s biggest mining project.

Once finished, it will raise coal exports from 50 million tonnes a year to 120 million tonnes, according to information on the project from a Queensland government website.

Environmentalists have argued that any expansion at Abbot Point would endanger the World Heritage-listed reef and destroy habitats.

Supporters have said the project would provide thousands of jobs and pump millions into the local economy.