China’s stock markets face a make-or-break week after officials rolled out an unprecedented series of steps over the weekend to prevent a full-blown stock market crash that would threaten the world’s second-largest economy.

The government is anxiously awaiting the market opening on Monday to see whether the new measures will halt a 30-per-cent plunge in the last three weeks, or if panicky investors who borrowed heavily to speculate on stocks will continue to sell.

In an extraordinary weekend of policy moves, brokerages and fund managers vowed to buy massive amounts of stocks, helped by China’s state-backed margin finance company that in turn would be aided by a direct line of liquidity from the central bank.

China has also orchestrated a halt to new share issues, with dozens of firms scrapping their IPO plans in separate but similarly worded statements over the weekend, in a tactic authorities have used before to support markets.

“After the 28 companies suspended their IPOs, there will be no new IPOs in the near term,” the China Securities Regulatory Commission (CSRC) said in a statement on Sunday night.

An online survey by fund distributor over the weekend, which polled more than 100,000 individuals, said investors believed stock indexes would rise more than 5 per cent on Monday.

But many of those polled didn’t think the bounce would last long.

“You’re going to need the central bank to open the floodgates to take us back to 4,500 points in Shanghai,” said an investment manager in Shanghai.

The Shanghai Composite Index was last at 4,500 on June 25, and is now trading 22 per cent lower.

China stocks had more than doubled in just 12 months, even as the economy cooled and company earnings weakened, resulting in a market that even China’s inherently bullish securities regulators eventually admitted had become too frothy.

But the slide that began in mid-June, which the CSRC initially tried to down play as a “healthy” correction after the fast run-up, has quickly shown signs of getting out of hand.

A surprise interest-rate cut by the central bank last week, relaxations in margin trading and other “stability measures” did little to calm investors, who sent shares down another 12 per cent in the last week alone.

China’s top leaders, who are already struggling to avert a sharper economic slowdown, seem to be losing patience.

Earlier, in a series of initial announcements on Saturday, China’s top brokerages pledged to collectively buy at least 120-billion yuan ($24-billion) of shares to help steady the market, and would not sell holdings as long as the Shanghai Composite Index remained below 4,500.

The China Mutual Fund Association said 25 fund companies also pledged on Saturday to buy shares. Another 69 fund firms said on Sunday they would do the same.

In addition, 28 companies that had been approved to launch IPOs all announced they had suspended their plans.

The U-turn is consistent with past IPO freezes in China when share markets were falling sharply, though they are usually spun as spontaneous company decisions, not as government directives.

Respondents to the survey thought news of an IPO slowdown or freeze would be the most welcomed on Monday.

On Sunday, state-owned investment company China Central Huijin said it had recently been buying exchange-traded funds and would continue to do so.

The combined effect of the policies is to signal to China’s army of retail investors, who conduct around 85 per cent of share transactions, that the government is now standing behind the stock market. But it is unclear whether even this will be enough to put a floor under prices or revive the rally.

Li Feng, a trader at Fortune Securities, said the amount of money that brokerages and fund managers vowed to put into the stock market was tiny compared with the size of leveraged positions still waiting to be unwound.

Some analysts suggest total margin lending, both formal and informal, could add up to about 4-trillion yuan.

Samuel Chien, partner of Shanghai-based hedge fund BoomTrend Investment Management Co., said he was ready to pile into blue-chip stocks, betting the new steps would trigger a rebound.

“Main indexes will rise. For the Shanghai Composite, the area below 4,500 is relatively safe now,” Mr. Chien said. “I have ample cash at hand, and surely will buy stocks this week.”

But people such as Shao Qinglong, a public service worker who has already lost more than one-quarter of his capital investing in stocks, told Reuters all he is waiting for is for the market to recover enough for him to break even.

“I didn’t sell at the peak because people all say the market will rise beyond 6,000 points,” Mr. Shao said. “I’m now waiting for the market to rebound so I can get out.”