Mine owner Energy Resources of Australia last night said the clean-up was "well advanced".

Chief executive Andrea Sutton said: "We are confident that we have the technical expertise to manage the incident."

She said monitoring at Ranger mine showed radiation dose levels were "well within" safe daily limit levels and water quality monitoring showed nearby creeks and billabongs had not been affected.

One of the four leach tanks ruptured and collapsed on Saturday, spilling up to 1 million litres of sludge containing a mixture of mud, water, uranium ore and acid near World Heritage-listed Kakadu National Park.

The accident came within a week of the collapse of an identical tank at Rio Tinto's uranium mine in Namibia, in southern Africa.

It is believed the Ranger tank was installed in the early 1990s.

The Ranger mine, which opened in 1981, has been shut down and all operations suspended until regulatory approval has been granted.

Environment Centre NT anti-nuclear campaigner Lauren Mellor said: "We're calling for operations to be shut down until a full safety audit can be completed.

"We're calling for ERA to withdraw its application for underground mining when we keep seeing these incidents increasing.

"The regulator needs to undertake a full review of operations to date and make its assessment based on past leaks, spills and incidents."

Ms Mellor said the mine had had at least 200 leaks in its history and its future looked bleak. "Maybe its time for Rio to get out of uranium mining," she said.

ERA general manager operation Tim Eckersley said the company was conducting its own investigation.