There has been a serious spill of contaminated slurry at a uranium mine near Jabiru in the Northern Territory.

The Ranger mine's operator Energy Resources of Australia (ERA) said a tank in the processing area of the mine failed at about 1:00am.

Workers discovered a hole in the side of the tank and were evacuated before the tank burst and "a mixture of slurry escaped".

The mine is surrounded by Kakadu National Park and is located about 230 kilometres east of Darwin.

Traditional owner groups said they are "sick with worry" about the potential environment impact, but ERA spokesman Tim Eckersley said there is no environmental emergency.

"They evacuated the area and at about 1:00am the tank basically split at the bottom and the processing slurry, which is a mixture of mud and water, has spilled out the bottom of the tank.

"That's the beginning of our processing operations, so it's a mixture of ground-up uranium ore and acid."

He said the material mostly spilled onto compacted earth, tarmac and drains.

"It's very impervious material so there's very little chance of it leaking into the soil there."

The company said earlier in a statement that the slurry moved outside the containment area, but was captured and contained on-site.

"As the material was contained within the processing area there is no impact on the environment surrounding the Ranger Project Area."

Investigation begins as anti-nuclear campaigners slam company

Federal Environment Minister Minister Greg Hunt has ordered an immediate clean-up and investigation.

A spokesman for the Minister said the leak has been contained and will have no impact on Kakadu National Park.

The Northern Territory Environment Centre is calling for an immediate halt to operations at the mine.

The centre estimates around 1 million litres of acidic radioactive material spilled from the processing tank.

Anti-nuclear campaigner Lauren Mellor said it is the third safety breach by the ERA in a month.

"Just within this month we've had an incident where a controlled vehicle was able to leave a secure area of the mine and was half way down the Arnhem Highway before it was located.

"We've had four barrels found in the Rural Area in Darwin, four barrels used to transport uranium were discarded with no explanation."

ERA said no-one was injured during the incident.

It is not yet known how long it will take for work to resume at the site.

The company has applied to the Federal Government for a large underground expansion of the mine, called the Three Deeps project. Indigenous traditional owners have not yet given their approval.