The China Securities Regulatory Commission (CSRC) is investigating Citic Securities for "allegedly violating the Supervision and Management Regulation for Securities Brokerages," the company said in a statement filed to the Shanghai stock exchange, where it is listed.
It did not give details of the investigation.
"Citic Securities will actively assist the investigation and release any progress in a timely manner. The company is operating normally," it added. Shares in in the firm dipped one percent Thursday.
They include general manager Cheng Boming, operations official Yu Xinli and the vice manager of its information technology centre, Wang Jinling.
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Eight Citic officials are assisting in police investigations, according to the news service.
The probe into the brokerage giant was announced as part of a wave of measures targeting the financial sector, following the spectacular meltdown of the Chinese stock market this summer.
After soaring 150 percent in one year, the Shanghai and Shenzhen bourses went into a tailspin in June that extended into August, tumbling nearly 40 percent despite massive intervention by the authorities at a cost of hundreds of billions of dollars.