China's former state assets chief Jiang Jiemin -- one of the highest-profile casualties of the country's anti-graft drive and an ally of ex-security chief Zhou Yongkang -- confessed to corruption at his trial Monday.

Jiang admitted his offences at the Hanjiang Intermediate People's Court in the central province of Hubei, the court said on its Sina Weibo microblog.

He is accused of bribery and abuse of power, the court said, adding that Jiang allegedly possessed "a huge amount of assets of unknown origin".

State broadcaster CCTV showed Jiang, with deep bags under his eyes, admitting his guilt.

"The facts of my crime are clear, the evidence is true and undeniable, and the Hanjiang court's lawsuit is objective," Jiang said according to the court statement, which added that he appealed for leniency.

"I confess to the facts of the crime without concealing anything. I admit my guilt and repent for my crimes," he said, adding that he had "damaged the image of the Party within the hearts of the people".

"For these errors, I am deeply, deeply repentant."

The hearing was completed on Monday afternoon and the judges "will select a date to announce the decision after deliberating in accordance with the law", the court said.

Photos posted by the court showed a stern-faced Jiang standing in the courtroom, clad in a dark blue jacket and with police officers towering over him on either side.

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

Jiang worked for decades in the petroleum industry and rose to become chairman of China National Petroleum Corp (CNPC), the country's biggest oil producer.

He has links going back to the 1980s with Zhou Yongkang, himself a former CNPC chief who went on to become China's hugely powerful internal security chief but was charged with bribery and abuse of power this month.

Prosecutors accused Jiang of "seeking profit in exchange for approving projects and granting promotions", the official Xinhua news agency reported.

They pointed to 14 instances where Jiang "solicited or illegally accepted money and goods either directly or through his wife", it said.

"Prosecutors pointed out that as of August 31, 2013, Jiang Jiemin's personal and family assets and expenses clearly exceeded his and his family's lawfully-earned income, and Jiang was unable to explain the source of the huge sum accounting for the difference," Xinhua reported.

Neither Xinhua nor the court immediately provided further details.

Jiang was tapped in March 2013 to run the State-owned Assets Supervision and Administration Commission (SASAC), which oversees China's many powerful state-owned enterprises.

But less than six months later, the ruling Communist Party's internal watchdog announced that it was probing him for alleged "serious disciplinary violations", a euphemism for official corruption.

According to state-run media, the move marked the first investigation of a member of the party's powerful Central Committee, which has about 200 members.

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.

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

Among them is former CNPC vice president Wang Yongchun, who was Zhou's assistant when he worked at the major Chinese oilfield of Daqing.

Another top CNPC executive, general manager Liao Yongyuan, was placed under investigation last month.

But critics note that China has failed to implement institutional safeguards against graft, such as public asset disclosure, an independent judiciary and free media, leaving the anti-graft drive open to exploitation for political faction-fighting.

The government has also stifled independent anti-corruption initiatives, jailing dozens of activists who had been involved in small-scale protests calling for government officials to disclose their assets.