Fallen Chinese politician Bo Xilai accused his former police chief, whose flight to a US consulate ignited a lurid scandal, of being a liar and a fraudster Sunday, the fourth day of a gripping corruption trial.

Before the judge abruptly adjourned for the day, Bo launched the scathing attack on Wang Lijun, whom the once high-flying politician had picked as his right-hand man in the southwestern megacity of Chongqing.

Wang turned accuser at a hearing in the eastern city of Jinan, but Bo said his testimony was "full of lies and fraud".

It was the latest flamboyant denunication by Bo, who has dismissed his wife Gu Kailai as "insane" and compared another prosecution witness to a "mad dog".

The Intermediate People's Court in Jinan is posting regular but delayed transcripts of the proceedings on its account on Sina Weibo, a Twitter equivalent, in a move hailed by state media as unprecedented transparency, although no independent verification is possible.

Wang was the key figure in court on Saturday, testifying against Bo over allegations of abuse of power.

He provided explosive details about the scandal triggered by the death of British businessman Neil Heywood, saying that Bo had punched him after he told the politician his wife was responsible.

Days later, Wang fled to a US consulate to seek asylum, blowing the scandal open.

"His character is extremely bad, he created rumours... and threw dust in the public's eyes," Bo said Sunday. "It's beneath legal credibility to present such a person as a key witness.

"Wang Lijun was lying during the trial and his testimony was not valid at all. His testimony was full of lies and fraud.

"He said I hit him with my fist instead of slapping him in the face. But the truth is I never learned the technique of Chinese boxing so I wouldn't be able to have that power."

Another prosecution witness, he said, was "trying to throw me under the bus and blame it on me".

Bo on Saturday admitted mistakes relating to the investigation into Heywood's killing and "some responsibility" for embezzled state funds that were transferred to one of Gu's bank accounts.

But he denies charges of abuse of power, bribery and embezzlement.

"The public prosecutor clearly has done a lot of work and I highly respect it," he said Sunday, but insisted the evidence against him had been "interpreted out of context".

Bo thanked the judge for caring about him, adding that he felt the court was "very humane and the proceedings very civilised".

The scandal erupted in advance of a generational shift of power atop the factionalised Communist Party, and Bo's feisty performance during his trial has astonished a public unfamiliar with the open airing of top-level intrigue.

The hearings are in stark contrast to previous Chinese political trials in which most defendants have humbly confessed their crimes in opaque court proceedings.

Revelations of private jet flights, luxury villas and rare animal meats have held Chinese Internet users spellbound, while Bo has showed open disdain for prosecution witnesses, including Gu.

He confessed to having had extramarital affairs and said Gu moved to Britain because she was angry with him, the court transcripts showed.

The trial was originally widely expected to last only two days but will resume for a fifth day Monday, the court said after adjourning following Sunday's morning session. It has finished hearing evidence on the charges themselves and will consider property seized during the investigation, it added.

Analysts still believe a guilty verdict and long prison sentence for Bo were agreed beforehand.

During the trial nothing has been said publicly of Bo's links with other top communist leaders -- even though he was once one of the 25 highest-ranking members of the ruling party and tipped to ascend even higher.

Bo's populist politics won supporters across China but alienated some top leaders of the factionalised party, who saw his brash approach as a return to a bygone era of strongman rule.

Xu Ming: prawn seller turned key witness against China's Bo
Beijing (AFP) Aug 23, 2013 - Bo Xilai's chief accuser at his corruption trial in China is a former prawn seller said to have made more than a billion dollars since linking up with the politician in the 1990s.

Born in April 1971 in the industrial port city of Dalian, Xu Ming spent his childhood in the countryside, the Hong Kong-based Mirror Books website said.

According to the website of Shide Group, the conglomerate Xu founded, he studied international trade at university.

His first job was a salesman in charge of Japanese clients at a prawn exporting firm in Dalian, according to Mirror Books, and he later established his own seafood trading company, although it was not a great success.

Shide Group was set up in 1992, around the same time that according to the Wall Street Journal Xu was introduced to Bo Xilai, then Dalian's mayor, and his wife Gu Kailai by a Taiwanese-American businessman, and they developed a close relationship.

The firm grew into a national conglomerate in the following eight years thanks to local government policies and contracts linked to Bo's plan to revamp Dalian into a shipping, fashion and information technology hub to impress the Party's top leadership, the paper said.

Shide now operates in sectors including construction material, petrochemical, finance, sports and home appliances.

In an example of how close Xu was to the Bo family, he accompanied Gu and her son Bo Guagua on a trip to Britain more than 14 years ago to scout out schools for the boy, according to the Wall Street Journal.

Bo is accused of accepting 20.7 million yuan ($3.4 million) in bribes from Xu, who testified for the prosecution on Thursday.

According to transcripts of evidence provided by the court trying Bo in Jinan, Xu gave the family millions over the years, including paying off a credit card bill of more than $50,000 run up by Guagua, and buying the boy an 80,000 yuan ($13,000) Segway scooter.

He said that when Gu expressed a desire to buy a villa in France, he provided $3.2 million for her to do so.

On its website Shide Group said that Xu was listed as the 85th richest person in China in 2010, worth $1.6 billion.

He faces charges of illegal business actions, the court in eastern China heard.