Environmental officers are working to save remote wetlands from a serious chemical spill after a truck rolled outside Kakadu National Park.

About 6,000 litres of sulfuric acid poured onto the Arnhem Land Highway near the turn-off to Fogg Dam Conservation Reserve, 100km from the entrance to the heritage-listed national park.

The spill is believed to be one of the largest in recent history and there are concerns about the environmental affect on surrounding wetlands.

"Environment officers have worked quickly to ensure the spill has been contained, the area has been bunded and the sulfuric acid confined to the roadside drain," said John Woinarski, the Northern Territory government's acting executive director of environment, heritage and the arts.

Mr Woinarski said work was underway to neutralise the split acid, which covers an area about 40 to 50 metres long and three metres wide.

"There is no threat to wetlands in Kakadu National Park and Fogg Dam Conservation Reserve," he said.

"The spilled product is being neutralised and it is expected that this will be completed shortly.

"The product is quite viscous and does not mobilise readily making containment effective."

The rear trailer on the road train - headed for the Ranger uranium mine located in the middle of Kakadu - overturned on the highway about 8.15pm (CST) on Thursday.

The acid is hazardous to touch or breathe and the spill has prompted calls for a review of the transport of dangerous liquids through wetland wilderness areas.

"It would be very difficult to clean up, I'm sure, and in a wetland I would imagine there is huge potential for it to spread over a vast area," Friends of Fogg Dam's president Heather Boulden told ABC Radio in Darwin.

Ms Boulden said there could be serious ramifications for birdlife if the acid seeped into the water supply.

Mr Woinarski said all efforts were being made to minimise the impact on the environment.

"Environmental officers will remain on site until we are satisfied that all actions have been effective in protecting the surrounding environment and community," he said.

Police are investigating the accident.