Haitong Securities. [File Photo: xinfinance.com]

China's securities regulator is investigating three big brokerages over alleged breaches of rules on signing client contracts.

Citic Securities, Haitong Securities and Guosen Securities are being investigated by the China Securities Regulatory Commission.

The probes are into contracts which the three brokers signed with clients on margin finances and short-selling.

Currently, their normal operations remain unaffected.

Shares of Chinese brokerages led a decline in A-share markets on Friday, with Citic down by the 10 percent daily limit.

Haitong shares dropped 4 percent before trading was suspended in Hong Kong.

The Chinese government has stepped up its clampdown on malpractice in the securities industry after a 5-trillion-US-dollar stock-market rout this summer.

The crackdown since the sell-off has ensnared executives and regulators.