Updated July 30, 2010 09:12:00

A road train carrying 57 tonnes of copper sulphate overturned on the Barkly Highway overnight. (Google Maps)

The only sealed link between the Northern Territory and Queensland remains closed after a chemical spill overnight.

Police say a road train carrying 57 tonnes of copper sulphate overturned on the Barkly Highway west of Avon Downs just before 10pm.

An exclusion zone stretching more than one kilometre has been set up around the spill.

Northern Territory Duty Superintendent Del Jones says motorists should avoid the area.

"The truck was heading off to Mt Isa mine with the copper sulphate," she said.

"However, the vehicle has blocked the road completely, both lanes of the Barkly Highway are blocked and it's unlikely they'll be cleared at least until midday today."

Barkly Divisional Officer Megan Rowe says equipment and fire officers are being brought in from Queensland to clean up the spill.

"My understanding from all advice is it's not too bad," she said.

"It's dangerous if you ate it or you breathed it in so we are taking precautions by blocking the road until we can get it cleaned up.

"But really you've got to get up close and personal with this stuff before it's going to cause you any damage."