Rio Tinto executive Stern Hu and three of his Chinese colleagues pleaded guilty on Monday to bribery charges during the first day of their trial.

Hu "acknowledged the truth of some of the bribery charges" laid against him, said Tom Connor, Australia's consul-general in Shanghai, who attended the hearing.

The other three are also charged with taking bribes and stealing commercial secrets.

Hu, an Australian citizen, is accused of taking bribes of 1 million yuan ($146,000) and $790,000. Connor said Hu had "made some admissions concerning those two bribery amounts".

The other three defendants - Liu Caikui, Ge Minqiang and Wang Yong - are charged with accepting bribes of up to 70 million yuan according to the court indictment, their lawyers said.

But the four accused will challenge the amount specified by the prosecutor, according to Tao Wuping, a lawyer for one of the accused.

The four also rejected some of the accusations made by prosecutors.

"Part of the charge should not constitute a crime," Tao said, referring to his client, Liu, who is charged with receiving 3.7 million yuan in bribes.

Wang admitted he was "guilty in part", his lawyer, Zhang Peihong, said.

Zhang said the $9 million Wang is accused of taking as a bribe was legitimate "profit from an iron ore deal".

The $9 million is part of the 70 million yuan that Wang is accused of taking as bribes, said Zhang.

"There are plenty of reasons to argue against the rest of the amount," Zhang added.

The trial, which is open only to several Chinese media organizations, is scheduled to last three days at the Shanghai No 1 Intermediate People's Court. The second part of the trial relating to commercial secrets will be heard in closed court.

Connor said all the defendants had an opportunity to put their views forward and address the evidence laid against them during the trial.

He also said the Australian government will issue a formal statement about the trial but did not specify when.

The trial marks the climax of a nine-month case that has strained relations between China and Australia, a key supplier of iron ore to Chinese steel mills.

Relations soured in June last year over a failed bid by State-owned Aluminum Corporation of China (Chinalco) to buy a $19.5 billion stake in Rio Tinto; and the arrest of Hu a month later.

Hu and his Chinese colleagues have been held in detention since July 5 last year.

Hu was Rio Tinto's lead negotiator in talks with Chinese steel mills to try and settle a price for iron ore from Australian mining companies.

Negotiations between Chinese steel firms and major international miners, including Rio Tinto, on iron ore prices have been at a standstill with the latter reportedly seeking price hikes of 90 percent or more this year.

According to Tao, the four defendants accepted bribes from some small- and medium-sized Chinese steel mills keen to secure long-term imports from Rio Tinto.

The Foreign Ministry has said the Rio Tinto case should not be deliberately politicized.

"It is just an individual business case. It should not be politicized or have a negative impact on China-Australia relations," Foreign Ministry spokesman Qin Gang has said.

Rio Tinto Chief Executive Tom Albanese, who was in Beijing at the China Development Forum on Monday, said: "This issue is obviously of great concern to us, as it would be for any company operating in China. I can only say we respectfully await the outcome of the Chinese legal process.

"We have enjoyed a good relationship with China for 50 years; only last year, we came upon some difficulties, which we are trying hard to resolve.

"Today, China is our largest customer. A positive relationship with this market is vital to the continued success of our company," he added.

He also said he had continued confidence in the long-term prospects of the Chinese economy.

Rio Tinto recently named a new top executive for China; and on Friday, it announced an agreement with Chinalco to develop an iron ore reserve in the West African country of Guinea.

Reuters and AP contributed to the story