The president of one of China's "big four" state-owned banks has resigned for personal reasons, the Agricultural Bank of China said, after reports he had been taken away in a corruption investigation.

The bank said Zhang Yun had stepped down in a statement to the Hong Kong stock exchange, where it is listed.

The announcement came a month after China's news portal Sina reported that Zhang, 56, had been taken away for questioning, as probes widen in the country's financial sector.

On Sunday, meanwhile, China's biggest brokerage Citic Securities told the Hong Kong exchange it had lost contact with two members of its executive committee -– Chen Jun and Yan Jianlin -- after media reported that they were embroiled in an investigation.

Chinese authorities have launched a series of investigations into the financial sector after a debt-fuelled stock market bubble burst in the summer in a rout that wiped out trillions of dollars of market capitalisations.

Citic Securities said two weeks ago that the company itself was being probed by the market regulator, the China Securities Regulatory Commission, following police investigations into several company executives for insider trading and leaking inside information.

By midday on Monday, Agricultural Bank was 0.91 percent lower in Shanghai and dipped 0.67 percent in Hong Kong.

Citic Securities dropped 1.32 percent in Shanghai and was 0.11 percent lower in Hong Kong.