China's stock market regulator said it levied fines of 28 million yuan or $4.4 million, besides administrative punishments, in eight cases of illegal share sales, amid a crackdown on irregularities in stock and futures trading.

A plunge in China's stock market over the summer and a surprise devaluation in its yuan currency have roiled global markets, stirring doubts about the government's ability to manage the economy.

The events have put global investors and policymakers on edge as China's economy appears set this year for its weakest performance in at least a quarter of a century.

The China Securities Regulatory Commission (CSRC) said on its website that the worst violation involved illegal share sales worth 183 million yuan ($28.76 million).

The CSRC also issued warnings to suspects after completing its investigations in another 11 cases involving violations such as insider trading and the spread of false information.

The campaign to find and punish those seen as responsible for the market sell-off started soon after the June turmoil.

Most analysts, however, attribute the crash to the bursting of a typical stock market bubble encouraged by official media and fuelled in large part by borrowed money.

The stock market regulator itself has been swept up in the country's biggest ever crackdown on corruption.

State media said the Communist Party sacked Zhang Yujun, the assistant chairman of the regulator, within days of an announcement that he was the subject of a graft investigation.

Chinese President Xi Jinping has launched a sweeping crackdown on deep-rooted graft since taking over the party's leadership in late 2012 and the presidency in 2013. Dozens of senior officials have been investigated or jailed.