There had been no breakthroughs until a recent investigation into an actress who obtained Hong Kong permanent resident status earlier this year, according to the Party newspaper report.

The actress, unnamed in the report, told investigators that Xu had offered her a large sum of cash and she had helped Xu deal with "personal activities" in Hong Kong.

An earlier report by the Hong Kong-based Ming Pao newspaper quoted unnamed sources as saying that the clampdown on Xu was related to an involvement with Huang Guangyu, the founder of Gome Electrical Appliances Holdings Ltd, who was once ranked as the richest man on the Chinese mainland.

Three Shenzhen vice mayors were also put under investigation around the same time in a snowballing inquiry into the criminal activities of Huang.

Huang was sentenced to 14 years and fined 600 million yuan (US$88 million) on May 18 for illegal business dealings, bribery and inside trading. He has appealed.

Huang's case has incriminated high-ranking officials, including Huang Songyou, a former vice head of the Supreme Court; Zheng Shaodong, a former assistant to the public security minister and Guo Jingyi, a former commerce ministry official.

Chen Shaoji, former police chief of Guangdong Province, and Wang Huayuan, once Guangdong's top Party disciplinary official, were both investigated for alleged involvement with Huang.