Auctioneers are hard at work selling tens of millions of dollars of coal mining machinery for just a fraction of its original market value.

The severe downturn in the Australian resources sector has led to a massive oversupply of equipment, and much of it is unsuitable for use in any other industry.

This means unwanted excavators, trucks and sundry heavy machinery will end up as scrap, if not sold at auction.

Was: $2.9m | Now: $15,000: Caterpillar 992C wheel loader

A 1991 Caterpillar 992C wheel loader that was sold at auction. ( Supplied: Hassalls )

The plant and equipment at auction at Charbon in central New South Wales was owned by Big Rim, a mining services contractor which collapsed after the miners it serviced also closed.

"At the moment we've probably got the worst downturn I've seen in 25 years," said Chris Hassall, whose company is conducting the auction.

Peter Turner's Gold Coast company Turner Engineering used to compete for contracts with Big Rim.

"I'd be interested in at least 50 per cent of what's here, and there are at least 100 machines here," he said.

Was: $1.4m | Now: $50,000: Hitachi EX1200 hydraulic excavator

A Hitachi EX1200 hydraulic excavator that was sold at auction. ( Supplied: Hassalls )

One of those machines was a large water tanker which Peter Turner was running the ruler over.

"It's not worth a lot. It's worth $75,000 or something, but you can't build the tank for that."

When the auction began the owners of a once-thriving business were hoping this fire sale would at the very least cover their debts.

"I used to work for this lot and now I've got my own company and I just thought I'd come out and see what's going," said a former Big Rim employee.

"I'm in the equipment business in Brisbane. I come down here, and whether I go home with anything or buy a cup of tea and a hot dog is yet to be decided," was the view of another tyre kicker.

And it wasn't just people in the coal industry looking for stuff on the cheap.

A wheat farmer from Nyngan in New South Wales was in the market for a bulldozer to dig dams on his property.

Was: $2.7m | Now: $46,000: Caterpillar D11N crawler tractor

A 1995 Caterpillar D11N crawler tractor that was sold at auction. ( Supplied: Hassalls )

"Some of the old equipment that was working in the last two years is now redundant, won't go back to work," said auctioneer Chris Hassall.

"We had 20 trucks in the Hunter Valley recently that 18 months ago were probably worth $600,000 each. We've just cut 'em up, returned about $40,000."

At auction, Big Rim's trucks were selling, but the only winners were the buyers.

Was: $900,000 | Now: $47,500: Caterpillar 775D rear dump truck

A Caterpillar 775D rear dump truck that was sold at auction. ( Supplied: Hassalls )

It's prices like these which help explain why shares of the Kerry Stokes-controlled Seven Group are less than half what they were two-and-a-half years ago.

Seven holds the largest Caterpillar franchises in both Australia and China.

Coupled with the mining downturn, with good second hand machinery so cheap, it is little wonder new sales have been hit hard.

Was: $200,000 | Now: $2,000: Large workshop with water tank

A large steel shed that was sold at auction. ( Supplied: Hassalls )

Contractor Peter Turner had been hoping to pay $75,000 for a water tanker, and in the end paid a little more at $77,500.

"It's got to be at least 30 per cent or 40 per cent under value. Closer to 50 most probably. It's been a very good day for me, very profitable day for me," he said.

It was a day which displayed the stark reality of a coal mining industry which has gone from boom to bust in a very short space of time.