Mining giant WMC Resources is confident it has contained a spill of 110,000 litres of radioactive liquid at its Olympic Dam uranium mine in South Australia's north.

South Australia's Environment Minister John Hill says WMC Resources has reported the spill of of process liquor, a weakly radioactive liquid used to extract copper and uranium from the ground.

The Environment Protection Authority is travelling to Olympic Dam to investigate.

EPA chief executive Paul Vogel says he has been told the spill happened at 7:30pm last night when a tank overflowed.

But he has been told the liquid did not enter the ground.

"We're treating this as a serious incident, but the fact that it is radioactive I guess raises the concerns to another level from the community's perspective," he said.

WMC spokesman Richard Yeeles says such incidents are rare.

"We don't have spills on a regular basis, I think this is the third one we've reported to the South Australian Government this year.

"Obviously any spill is a concern but we believe we operate Olympic Dam in a very safe and envionmentally responsible way."