Australia urged China to allow diplomatic access to the trial of four Rio Tinto staff charged with commercial spying, in a case that begins next week.

Prime Minister Kevin Rudd said his government would do everything possible to help the Anglo-Australian miner's staff who were arrested in July and since held in detention.

Rudd said the outcome of the case, which has also stoked investor concerns about China's murky legal environment, would be closely watched.

[Kevin Rudd, Australian Prime Minister]:
"The world will be watching how this particular court case is conducted."

China arrested the four staff, including Australian Stern Hu, for bribery and stealing business secrets, which could bring sentences ranging from three to 20 years.

The case has strained bilateral relations and put a cloud over an industry that has thrived as Chinese demand for commodities has soared.

Mining giant Rio says the four did nothing wrong, while Rudd said Thursday the government would look out for its citizen.

[Simon Crean, Australian Foreign Minister]:
"The Australian government will do all that is necessary to support Mr. Hu's interest.”

China is Australia's biggest trade partner, with commerce hitting $53 billion last year, and Canberra supplying over 40 percent of Beijing's iron ore imports.