China's two stock exchanges have slapped trading limits on more than 20 accounts as the market regulator on Friday announced a crackdown on computerised "programme trading", which it blamed for recent volatility.
The moves are the latest steps by authorities to try to stem a market rout that saw the benchmark Shanghai Composite Index plunge more than 30 percent, raising worries over reforms and the possible impact on the wider economy.
The China Securities Regulatory Commission (CSRC) said it was investigating institutions and individuals for programme trading, which had amplified "big fluctuations" on the stock market, according to a statement on its website.
The practice typically involves automated transactions carried out by computer at high speed on a large number of stocks.
The Shanghai and Shenzhen exchanges had put limits on 24 accounts for influencing stock prices and investors' decisions, the CSRC statement added, without naming the account holders or detailing the restrictions.
The CSRC has already announced probes into "malicious" short-selling -- a bet prices will go lower -- and what it called "concentrated" selling, which caused an 8.48 percent plunge in the Shanghai market on Monday, the biggest one-day fall in eight years.
Other moves by authorities in the wake of the falls -- which began last month -- include banning shareholders with more than five percent stakes from selling stock and funding the state-backed China Securities Finance Corp. to buy shares.
Analysts say trading is likely to remain volatile with many expecting the benchmark Shanghai index to fall further.