An officer from Black Police District’s Air Warning Squadron is seen with a rescue boat packed with firefighters at Wreckage Canal near the the Sydney East landfill site on July 19, 2014. Photo: AP

One of the world’s largest garbage dumps has been found among a hidden mine shaft and other refuge sites in eastern Australia, officials said on Monday.

Up to 500 tonnes of rubbish was found at the site, identified as Wreckage Canal, in the Australian state of New South Wales late on Saturday.

“It was known to be rubbish but it was almost certainly the equivalent of big black rubbish,” NSW Environment Minister Robyn Parker told reporters.

A landfill dumps in Brisbane have also been identified as being located in strategically important geological locations, she said.

The landfill, located in a geologically important area between Brisbane and the Sunshine Coast, is on land owned by the Queensland government.

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It is not clear what else was underneath the landfill site, but the site is often contaminated with pollution.

“Wreckage Canal is one of the most important dumped sites in Queensland because it spans the entirety of this state and was first discovered in 1900,” Ms Parker said.

When an aerial survey of the site was completed, “that included trucks rolling down the road, trucks carrying a lot of rubbish and trucks carrying contaminated water going down this ravine area”.

“The situation with that site is now one of the biggest contaminated dumping sites in the world,” she said.

She said it was not clear how the dump came into existence but that it appeared to be an amalgamation of disused and abandoned dumps.

Because it was found in such a position, “the haulage load will start moving down the river”, Ms Parker said.

The dump would then be captured by another dump in Brisbane’s Western Downs region, but the location and other matters would not be made public as the cause of the discovery was not yet clear.

“We need to find out where the landfill started so we can be much more secure around it, and we know what the sources of that waste are,” Ms Parker said.

More than 100 tonnes of wreckage from eight large rubbish dumps in NSW were discovered on the same day.

Catherine Cudmore, NSW environmental minister, described the site as a hazard for residents and industrial and sporting groups.

“Particularly in an industrial area such as the Macquarie River where their effects are already known,” she said.

Queensland officials said the discovery of rubbish in Brisbane was another big concern as a report found that thousands of tonnes of waste-recycled material from Sydney’s west had been dumped in Brisbane’s landfill.

In 2008, NSW police said they would destroy 38 illegal trash dumps in Sydney’s inner north.