A former senior executive of China's largest oil producer denied most corruption charges at his trial, state-run media reported Tuesday, a rare example of defiance in a country where almost all criminal defendants are convicted.

Tao Yuchun, ex-president of a gas subsidiary of state-owned China National Petroleum Corp (CNPC), was accused of abuse of power, embezzlement, taking bribes and seeking illegal gains for relatives and friends totalling around 300 million yuan ($48 million), the Southern Metropolis Daily said.

He only admitted the final charge but rejected all the others at his trial on Monday in Zhuhai, in the southern province of Guangdong, it said.

Tao smiled at his friends and relatives in the gallery at the start of the hearing and addressed the court throughout in the dialect of Shandong, his native province in eastern China, rather than using official Mandarin, the newspaper added.

His performance was a marked contrast to the norm in China, where the conviction rate is 99.93 percent and most defendants adopt a cooperative and compliant attitude in court as they seek to secure leniency in exchange for confession.

Chinese courts are closely controlled by the Communist Party, as is reporting on sensitive trials, and a guilty verdict for Tao is effectively a certainty.

Jiang Jiemin, China's former state assets chief and an ex-chairman of CNPC, confessed to corruption at his trial on Monday, television pictures showed.

Jiang is regarded as an ally of Zhou Yongkang, himself a former CNPC chief who went on to become China's hugely powerful internal security chief but who was charged with bribery and abuse of power this month.

President Xi Jinping, who took office two years ago, has vowed to oust corrupt officials all the way from low-level "flies" to high-ranking "tigers" amid fears graft could threaten the party's hold on power.

But in the absence of systemic reforms, critics say the drive is open to being misused for internal political purposes.

Zhou and a host of his disciples have been detained and stripped of their party membership since 2013, amid official media allegations of an "oil faction" in the party.