The government told state companies and executives to buy shares, raised the amount of equities insurance companies can hold and promised more credit to finance trading.
Hundreds of companies have halted trading in their stock after emergency measures announced last weekend failed to stop a rout that has dragged down the benchmark Shanghai Composite Index by more than 30 per cent since early June.
The Shanghai index lost another 5.9 per cent on Wednesday despite the new measures and Hong Kong's Hang Seng index closed down 5.8 per cent after diving as much as 8.5 per cent earlier in the day.
Greece's debt crisis has unsettled Asian stock markets but the losses in China are driven entirely by internal factors. Beijing fostered a market boom over the past year, but with Chinese economic growth slowing, it had little basis in reality. Prices began collapsing after unrelated changes in banking regulations made investors in the rumour-fueled market suspect the government could withdraw its support. Regulators also tightened lending to stock investors, adding to their fears.
The decline in Chinese stock prices threatens to fuel 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 have plunged in value say they will no longer buy shares.
Little more than a month ago, China's stock market was the best performing in the world. The boom began after state media said last year stocks were cheap, which led investors to believe Beijing would prevent prices from falling. The Shanghai index still is up 70 per cent from one year ago but novice investors who piled in just before the peak hold shares that are worth less than they paid.
Financial literacy is limited in a society where the mainland's first communist-era stock exchange opened in Shanghai only in 1990. Brokerages offer classes in trading but a culture of commentators who preach the gospel of low-risk, long-term investing has yet to develop. Many small investors rely on rumours or tips from friends in a market rife with complaints of insider trading and fraud.
"The central government made considerable reputational investment in the rally over the last year, particularly via ample cheerleading from state media," said IHS Global Insight economist Brian Jackson in a report. Official support "is likely to remain extraordinary," he said, but it will be hard to revive flagging investor enthusiasm.
On Wednesday, the Cabinet agency that oversees China's biggest state-owned companies said it had told them to avoid selling shares and to buy more "in order to safeguard market stability."
In a separate order, the securities regulator told directors, executives and senior managers of publicly traded companies who have sold shares in those companies within the past six months to buy them back and said they are barred from selling. It said they are required to buy more if the price falls by more than 30 per cent in the next 10 days.
The insurance regulator said the proportion of their assets Chinese insurers are allowed to invest in stocks will be increased to 40 per cent from 30 per cent. The amount of a single blue-chip company's shares that an insurance company can buy will increase to 10 per cent from 5 per cent.
The central bank said it will provide "ample liquidity to support stock market stability" through a state-owned company that lends to brokerages to finance share purchases, a practice known as margin lending. The People's Bank of China statement was read on state TV's national midday news.
Chinese authorities have tried to reassure investors the decline is normal following the boom that saw the Shanghai index soar by more than 150 per cent beginning in late 2014. The flagship ruling party newspaper, People's Daily, said Monday the economy can maintain steady growth and provide "solid fundamentals" for "healthy development of capital markets."
Jackson, of IHS Global Insight, noted a survey by the Southwestern University of Finance found 8.8 per cent of households participated in the stock market in the second quarter of this year, up from 6.1 per cent in the first quarter. According to the newspaper China Business News, the latest percentage is the equivalent of 37 million households.
"That confirms that a substantial number of households rushed in just as valuations were peaking, but also that the total exposure of private households in China is relatively low compared to Western countries, where often a third or more participate in equity markets," said Jackson.
Also Wednesday, a group of 21 state-owned brokerages that pledged last weekend to buy blue chip stocks — or shares in major state companies — said they will increase the size of a fund to finance that from 120 billion yuan ($19 billion) to 260 billion yuan ($42 billion).
The pledge helped to boost shares in major banks and other government companies such as PetroChina Ltd., Asia's biggest oil and gas producer. Their prices rose by up to 10 per cent on Monday and Tuesday, but shares in smaller companies that are not included in the pledge have fallen.
A state company that provides credit to brokerages said it had injected a total of 200 billion yuan ($32 billion) into five mutual funds to buy shares. It said that would help to support prices of smaller companies because those funds can buy any shares, not just blue chips.
Some 787 companies suspended trading on the exchanges in Shanghai and the southern city of Shenzhen by the end of trading Tuesday, according to China Business News. It said more requested a suspension later, raising the total to more than 1,000 — the equivalent of almost 36 per cent of the total of 2,802 companies traded in Shanghai and Shenzhen.
Hong Kong shares in which trading was suspended included Sinopec, China's No. 2 state-owned oil company.