Fifty-two hectares will now be cleared to make way for the Brandy Hill Quarry extension in Port Stephens, after Environment Minister Sussan Ley twice delayed her decision as calls to reject the proposal grew.

Australian music royalty Jimmy Barnes and Olivia Newton-John, as well as comedian Magda Szubanski, are among the project's high-profile opponents.

"The poor koalas are copping it again," Barnes tweeted in September.

"You'd think after last year's bushfires, bulldozing 52 hectares of their habitat wouldn't be on anyone's radar."

NSW Environment Minister Matt Kean also appeared to publicly back away from his own government's approval of the project, calling for his federal counterpart to closely consider her decision in light of the bushfires.

But Minister Ley on Tuesday said she had approved the project because the quarry company, Hanson, had promised to establish a 74 hectare koala habitat corridor - 22 hectares more than the venture would destroy.

"I recognise that the proposal has been subject to a high profile public campaign that has tapped into the genuine concerns we all share about koalas and bushfire impacted areas," Minister Ley said in a statement.

The concern prompted her department to commission independent assessments of koala numbers at the site, she said, which found only "one or two" koalas within the area to be cleared.

"Brandy Hill's expansion ... will not rob the area of critical koala habitat," Ms Ley said.

"This is not a region where bushfires have impacted local populations or habitat, the area to be cleared is not a site that is supporting resident breeding populations, and ... I have approved the proposal."

The new koala habitat corridor will actually create more habitat for the species, she says, and will include bushfire buffer zones, and protection for the animals from dogs and cars.

Australian Associated Press