Chinese shares tumbled sharply in Monday's morning session, as the government continues to investigate allegations of market manipulation.
The benchmark Shanghai Composite Index, the smaller Shenzhen Component Index and the NASDAQ-style ChiNext Index dipped 2.61 percent, 2.39 percent and 3.09 percent, respectively, in the morning session.
All key indices declined more than 3 percent, retreating into negative territory, again, despite substantial gains on Thursday and Friday.
The market's weak performance on Monday occurred in spite of government intervention to stabilize the volatile stock market.
Since June, measures have heavily featured the pumping of funds into the system.
Despite this, key indices have continued to nosedive over the last fortnight, and some analysts are calling on policymakers to use a wider range of tools instead of merely injecting liquidity.
On Sunday, a journalist, an official with China's securities watchdog and four senior executives of CITIC Securities, China's largest brokerage, were placed under "criminal compulsory measures" for suspected market manipulation and trading violations.
This is the toughest response since the market began to fall in mid-June.
Wang Xiaolu, journalist with Caijing Magazine, is suspected of colluding with others, and fabricating and spreading fake information.
Liu Shufan, an official with the China Securities Regulatory Commission (CSRC), was held over allegations of insider trading, accepting bribes and forgery.
CITIC Securities' Xu Gang, Liu Wei, Fang Qingli and Chen Rongjie were held for suspected insider trading.
Compulsory measures can include arrest, detention, summons, bail pending trial, or residential surveillance.
On Friday, a CSRC spokesperson said the commission had referred 22 cases of suspected market manipulation, insider trading, fabricating and spreading false information to the police, bringing the total number to 48 this year.
Also on Friday, the China Financial Futures Exchange announced it had raised margin requirements on stock index futures to 30 percent of the contract value, in a bid to curb speculation.
The government appears to be paying greater attention to the stock market rout, with Premier Li Keqiang telling the State Council on Friday that financial stability was significant to the broader economy.
"It is important to foster an open, transparent capital market of long-term stability and ensure its sound development," said Li.
He also added that risk management must be improved to prevent regional or systemic risks.
