China's securities regulator has announced the first penalties for violators of a ban imposed in July on stock sales by major shareholders as part of frantic government efforts to stem a slide in prices.

Four investors, five institutions and eight executives were fined a total of 28.4 million yuan (US$4.5 million), the China Securities Regulatory Commission said. It gave no details of their identities.

The announcement, dated Tuesday, said they were the "first batch" of penalties under the July 8 rule, suggesting more might be announced.

The ban on sales by shareholders who own more than five per cent of a company was one of a flurry of measures imposed after China's main market index fell 30 per cent beginning in early June.

The violators' sales "seriously undermined the market order and damaged investor confidence," the securities commission said in a statement.

Other emergency measures included multibillion-dollar stock purchases by a state-owned brokerage and a finance company.

Authorities have reduced the scale of those purchases but have set no date for easing the ban on sales by big shareholders.

The stock market slump fuelled political tensions and set back Communist Party plans to use financial markets to make China's state-dominated economy more productive. The party wants to encourage stock ownership, but small investors whose holdings plunged in value have said they will no longer buy shares.

In a separate case, the police ministry announced September 15 that the general manager and other executives of China's biggest stock brokerage, state-owned Citic Securities Limited, were under investigation on suspicion of insider trading and leaking sensitive information.

On September 16, the ruling party's discipline agency said the deputy chairman of the securities commission was suspected of "serious violations of discipline", the official term for corruption.