Senior Constable Graeme Ferguson, of Balclutha, said six rolls of Powergel Buster high explosive were found in an abandoned car near a forestry block on Wangaloa Rd.
The area was used frequently by walkers, mountain bikers, horse riders and off-road motorcyclists, he said.
Powergel Buster is a packaged emulsion explosive capable of creating devastatingly powerful detonator-sensitive explosions.
The explosive is white with a firm putty-like consistency, and is stored in rolls that appear similar to dog food rolls.
Snr Const Ferguson said the explosive was normally used in mining, and by farmers for clearing tree stumps and rocks.
"It is an explosive, and although it needs a detonator or initiating device to explode, it becomes more unstable with age.
"These rolls look very old.
"They've got potential to be volatile."
The Orica Mining Services website said Powergel Buster could be initiated by extremes of shock, friction or mechanical impact and, as with all explosives, it should be handled and stored with care.
The site recommended storing the explosive in a suitably licensed magazine which would give it a safe storage life of up to 12 months.
However, exposure to hot or cold extremes could cause the product to deteriorate prematurely.
Snr Const Ferguson said the explosive material was discovered about 11.30am yesterday by a local landowner.
He believed it had been dumped there in an old car wreck about a week earlier.
"It's very irresponsible behaviour. There are channels these people could have gone through to get rid of this stuff safely. They shouldn't have just left it in a public place."
New Zealand Army experts drove down from Christchurch yesterday while police guarded the scene.
The material was disposed of without incident last night.
Snr Const Ferguson said any assistance in locating the people who put the explosives in the car would be gratefully appreciated.
