The closely-watched trial of four employees from Anglo-Australian mining giant Rio Tinto has opened in Shanghai.

Australian national Stern Hu, the head of Rio Tinto's Shanghai office, and three Chinese staff are being tried on charges of stealing secrets and offering bribes.

The trial opened on Monday in Shanghai's No 1 Intermediate People's Court and is expected to last three days.

The case has strained ties between Australia and China and is being viewed as a barometer of China's handling of foreign business and the transparency of its legal system.

The four were arrested last year during contentious iron ore contract negotiations.

Reporters outside the court said some journalists, mostly from Chinese state media, were allowed in to cover the opening session.

However, China has said the hearings on the industrial secrets charges will be held behind closed doors, raising questions from Australian officials over whether the men will get a fair trial.

Ahead of the trial Australia's prime minister, Kevin Rudd, warned China that the world would be watching the case "very closely".