Foreign journalists were also barred from the trial.

The maximum penalty for commercial espionage is seven years in prison, while a bribery conviction could see them jailed for up to five years.

Few details of the allegations against China-born Australian citizen Hu, the head of the company's iron ore business in China, and Wang Yong, Ge Minqiang, and Liu Caikui have been released.

The four men were formally arrested in August and have not been allowed to make any public comment.

Guilty pleas

On the first day of hearings last Monday, the four executives pleaded guilty to charges of taking bribes, but defence lawyers said the amounts taken were far smaller than the sums prosecutors allege.

Parts of the trial were closed to Australian consular officials [Reuters]

Prosecutors said the bribes reached 6.46 million yuan ($946,300) for Hu, and 75 million yuan - including $9m from steel tycoon Du Shuanghua - in the case of Wang, head of a separate iron ore sales team.

Liu, who was accused of taking the lowest amount of kickbacks among the four, was the only one to plead guilty to infringing commercial secrets.

The admissions of bribe-taking have been seen as a blow for Rio Tinto, one of the world's largest miners, at a time when it seeking to restore good relations with China.

After initially staunchly defending its staff, the company recently urged the court to handle the case in a quick and transparent way.

The case is seen by many working in China as a signal that the government is subjecting foreign companies to increasingly close scrutiny, raising the risks of running foul of secrecy laws that are, themselves secret.

The four employees were arrested shortly after the collapse of tense iron-ore contract talks, and just weeks after Rio snubbed a major investment by state-run Chinalco.

The Shanghai court will also rule on a second case on Monday, that of Tan Yixin, an executive at Shougang Corp, China's eighth-largest steel mill, who was detained around the same time as the four Rio employees.