A billionaire Chinese petrochemical entrepreneur on Monday became the fifth senior industry figure in a week to become enmeshed in a corruption investigation that continues to reach higher into China's political and economic elite.
The entrepreneur, Hua Bangsong, 47, is "now assisting the relevant authorities in the P.R.C. in their investigations," according to a filing made late Monday to the Hong Kong Stock Exchange by Mr. Hua's company, Wison Engineering Services.
(Read more: China expands inquiry on graft to oil industry)
A crackdown on corruption in China has intensified in recent weeks, focusing on the oil industry. Mr. Hua's company is one of the largest nonstate contractors to the oil and gas industry in China, and counts the China National Petroleum, or C.N.P.C., as one of its biggest customers.
Last week, four senior managers of C.N.P.C. and its subsidiary, PetroChina, were removed from their positions and placed under investigation on suspicion of what an official statement called "grave violations of discipline," almost always a reference to corruption, bribe-taking or embezzlement.
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The investigation appeared to escalate on Sunday when Jiang Jiemin, director of the powerful commission that oversees the government's stakes in the largest nonfinancial state companies in China, was also cited on suspicion of "grave violations of discipline," according to a statement on the Web site of the party's Central Commission for Discipline Inspection. Mr. Jiang had been general manager, then chairman of C.N.P.C. until March.
Mr. Jiang, a full member of the party's elite Central Committee, became the highest-ranking official to be publicly cited for scrutiny since President Xi Jinping came to power last November. Mr. Xi pledged to battle official corruption at levels high and low, taking down "tigers and flies."
People with knowledge of the matter who cited senior officials said the investigations were centering on associates of Zhou Yongkang, one of China's most senior leaders, who retired in November after five years in charge of the state security apparatus and had been a longtime oil executive and general manager of C.N.P.C.
In announcing that Mr. Hua, the entrepreneur, was assisting the investigations in China, Wison sought on Monday to defend its business ties to PetroChina.
"The company operates legally," Wison said, adding that prior to its December listing on the Hong Kong stock market, it "completed the necessary compliance check."