Southwest China's Yunnan province is emerging as the center of an epidemic of corruption connected to the case of ex-security chief Zhou Yongkang.

The investigation of a series of cases involving alleged corruption in the province indicates that it is squarely in the central government's sights, along with Sichuan, Shanxi and Jiangxi provinces, where a majority of officials put under investigation reportedly had ties to Zhou, sources told China Business News.

Cases include those of Bai Enpei, former Party chief of Yunnan province; Shen Peiping, the province's former vice-governor; Yao Tangwen, former director of the Yunnan Provincial Statistics Bureau; and Chu Zhongzhi, Party chief of Dali city.

So far, the anti-graft effort in Yunnan has focused on land and resources, transportation, construction and education.

Zhou's power base was in Sichuan, but his influence on officials in neighboring Yunnan province was also deep. Investigated officials Shen Peiping and Bai Enpei were reported to be Zhou's close associates.

Yunnan has abundant natural resources. Its reserves of aluminum, lead, zinc and tin are the largest in China. Investigations have targeted officials that were in a position to handle resources illegally.

According to China Business News, reconstruction and the cheap sale of the Lanping Lead-Zinc Mine and Dulong Tin Mine were breakthroughs in the series of corruption cases.

In early 2000, Zhou Yongkang's mining tycoon friend Liu Han, former chairman of Hanlong Group, the largest private enterprise in Sichuan, reportedly wanted to acquire the Lanping mine. At the time, Bai Enpei was a nominee for Party chief of Yunnan province, and Zhou was Party chief of Sichuan.

With help from the two, Liu got control of the mine at a bargain rate of 150 million yuan ($24 million) for 60 percent of the Lanping mine, the largest one in Asia with market value in the hundreds of billions of yuan.

Liu was sentenced to death in August for his mafia-like acts, including instances of injury and murder.

But no hearing in the case of Liu's wife, Yang Xue, who is suspected of shielding him, has yet been opened, primarily because Yang's case is tied in with those of Zhou Yongkang, Zhou Bin (Zhou's son) and Bai Enpei, China Business News reported.

Dulong Tin Mine is also connected with the investigations of many officials, among them Zhang Tianxin, former Party chief of Kunming.

"High-voltage pressure will be applied to curb corruption," Huang Shuxian, vice-secretary of the Communist Party of China Central Commission for Discipline Inspection was quoted by Xinhua News Agency as saying.