A WHOPPING 5.5kg gold nugget worth up to $300,000 has been found in bush near Ballarat.

The "incredibly rare" nugget was found 60cm underground by a prospector, who wishes to remain anonymous, on Wednesday.

Ballarat Mining Exchange Gold Shop owner and dealer Cordell Kent said the prospector heard a faint noise on his detector and removed a dense pile of leaf mulch before he started digging.

"He thought he had detected the bonnet of a car when he saw a glint of gold," Mr Kent said.

"He cleaned the top of it and the gold kept expanding and expanding ... he saw more and more gold ... he couldn’t believe what he was seeing."

The nugget is worth about $282,000 in weight, but has an added premium because it is rare to find one over a kilogram, Mr Kent said.

"I have been a prospector and dealer for two decades, and cannot remember the last time a nugget over 100 ounces (2.8kg) has been found locally.

"It’s extremely significant as a mineral specimen. We are 162 years into a gold rush and Ballarat is still producing nuggets - it’s unheard of."

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The nugget was found with a state of the art metal detector called a Minelab GPX-5000, marketed as the best in the world, which Mr Kent said made the find possible.

"There has been many prospectors that have walked past the exact place where the nugget was found and have missed it with an ordinary detector and did not have the technology to find it…that’s why this guy found it.

"This detector he used is the best there is, it goes deeper and further into the ground, better than others."

Mr Kent said the find was unique with the nugget measuring at its longest 220mm, 140mm wide and 45mm at its deepest point.

He said the find would increase the enthusiasm of existing and new prospectors to Ballarat and the central Victorian goldfields.

Mr Kent said the prospector's new fortune would be well spent.

“He’s a person that really deserves it.

“He rushed to tell his wife when he found it and she didn’t believe him at first. He is going to pay off a lot of bills and pay off his house - it’s a real life changer.

“We’ve got 800 local prospectors on our records. I cannot remember the last time we saw a nugget of this size.”

Jessica.evans@news.com.au