China's regulators are taking fresh steps to try to quell volatility in the country's financial markets.
Investors holding stakes of more than 5 percent are not allowed to sell shares in the next six months.
The new rule from the country's securities regulator is intended to relieve pressure on the stock market.
Despite efforts to stem the losses, the dramatic sell-off in China's main stock market continued on Wednesday, with the Shanghai Composite plunging 6.8 percent.
That took share values nearly 30 percent below their June peak.
Yesterday, another 500 listed firms said they would stop trading their shares in an effort to insulate themselves from the meltdown.
Around 1,300 firms have halted trading, almost half of China's main shares.
IG chief market strategist Chris Weston dubbed the sell-off "Black Wednesday".
"For the first time, The China Insurance Regulatory Commission (CIRC) has admitted there is genuine 'panic selling' underway.
"When we see around 90 percent of the market suspended or falling by their daily limit (while further measures have been taken to limit the influence seemingly exerted by futures traders) you know things are becoming less rational," he said.
Investors in China rely on margin financing from these brokerages to borrow money to buy stocks.
Insurers were also given the go-ahead to invest more in blue chip stocks - with the industry watchdog raising limits from 5 percent of their total assets up to 10 percent.