Eighteen people have been fined after authorities busted an illegal holiday shack hidden deep inside a protected national park.

The cabin was secretly constructed on Curtis Island, near Gladstone, Queensland, without any approvals.

It effectively turned part of the Great Barrier Reef World Heritage Area into what officials slammed as a “private playground”.

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The off-grid structure featured solar panels, rainwater tanks, bunk beds and cooking facilities, even a verandah and barbecue area, allowing “guests” to stay comfortably in the remote wilderness.

But the luxury came at an environmental cost.

Illegal 4WD tracks were carved through fragile dune ecosystems to access the site, while trees were illegally felled by hand and used to build the hut and surrounding camp structures, authorities said.

The Department of Environment, Science and Innovation (DESI) launched a compliance investigation after receiving community reports and surveillance footage.

“Curtis Island is a national park, not a private playground,” DESI said.

“We take these matters seriously and our dedicated officers work hard to protect Queensland’s precious natural places.

“We will not hesitate to prosecute people who disregard the rules.”

The investigation uncovered the site was linked to other prohibited activities including hunting with firearms and unauthorised vehicle use inside the park.

Curtis Island, accessible only by ferry from Gladstone, is popular with 4WD tourists for its pristine beaches, bushland and fishing spots.

The island is also home to crucial turtle nesting grounds, rare birdlife and fragile dune systems.

Authorities said the illegal hut was built near protected areas where 4WD tracks, rubbish and noise risk disturbing nesting turtles and damaging fragile dune systems.

Camping on Curtis Island is only permitted at designated sites with bookings.

Fires are completely banned, and all structures — even temporary ones — are strictly prohibited under the Nature Conservation Act 1992.

DESI fined 18 people — including the accused builders and visitors caught at the illegal site — a total of $7,606.

“Queensland’s national parks are for everyone to enjoy, not for a select few to exploit for personal gain,” the department warned.

Officials are now urging anyone with information about unauthorised activities to come forward and help preserve Queensland’s unique natural heritage for future generations.