In the past few months, overseas political gossip websites have been linking the 50-year-old with former security tsar Zhou Yongkang who is under Communist Party investigation for corruption.

Wu has not been seen in public since May 22, the same day he donated HK$10 million to the government of Yaan in Sichuan province. The city was hit by a 7-magnitude earthquake in April, the official reported.

Although he is believed to be one of the richest men in Sichuan, which is Zhou's power base, Wu has shied away from the limelight.

His Hong Kong company address listed in the company directory belongs to the Association for the Promotion of Global Chinese Traders Fraternity, and he was once its vice-president.

A woman in the association's office said on Friday she had never heard of Wu or his company despite having been with the organisation for several years.

Calls to a number believed to belong to Wu were not answered. The person named in the registration of his Chengdu company, Wang Zhiqiang , and who reportedly helped him manage businesses for over a decade, declined to comment when reached by telephone.

In an earlier interview with the mainland's newspaper, Wang said he was only "a professional manager and a nominal legal person", who "doesn't hold stock of the company and doesn't know the current status of Wu Bing".

Since 2001, through different proxy companies, Wu has pursued a handful of deals in Sichuan, including the construction of two hydroelectric stations in the region worth billions of yuan, according to the mainland's magazine.

Another financial magazine, , has suggested Wu has a close relationship with Guo Yongxiang , Sichuan's disgraced deputy governor and a former secretary to Zhou.

Guo, who was in charge of water utilities in the province, and was once chairman of the literary federation in the province, was detained in June. The report said Wu has invested in a number of hydroelectric projects.

The report cited unnamed sources as saying Wu's detention was part of the government's new campaign against corruption in the oil industry.

It said Wu's Beijing-based Zhongxu Sunshine Energy Technology, which is registered under the name of a person named Zhao Ming, signed contracts with China National Petroleum Corporation (CNPC) to construct and manage half of its 16,000 fuel stations across the country.

Zhao didn't respond to calls for comment.

Weeks after Wu is believed to have been detained, the party's Central Commission for Discipline Inspection announced it was investigating five senior officials with the CNPC, including its former chairman Jiang Jiemin .

The Chinese-language version of reported on Friday that the investigation allegedly started after disciplinary watchdogs learned that a trust fund, based in Los Angeles, had made about US$800 million from a suspect deal with the company. The owner of the fund is surnamed Wang, it said.

The report did not give a full name.