Since the 2008 financial crisis, China’s relatively strong economic growth has helped propel a global recovery. And in theory, economic damage from even a precipitous market drop should be contained — Chinese stocks are still much higher than they were a year ago.

But the Chinese economy was faltering even before its markets began plunging last month. Many investors are now worried that further declines in stock prices could depress Chinese consumer sentiment and demand, as well as growth prospects, with ripple effects around the globe. China is the world’s biggest importer of oil and other raw materials, and commodity prices and stocks of commodity producers were hit especially hard in the sell-off this week.

Even in the market-oriented United States, stock prices are not entirely free from government influence. The Federal Reserve typically floods the market with liquidity and eases monetary policy at times of crisis and market panic. During the financial crisis, United States regulators banned the short sale of stocks of financial companies in the belief that short-selling, in which investors borrow shares hoping to sell them later at a lower price, drives down prices. (Subsequent studies concluded that the effort was futile.) China is also restricting short-selling.

But the United States has never embarked on the direct purchase of stocks in an effort to prop up the entire market, and such measures elsewhere have been rare. Probably the closest parallel is Japan, where the central bank this year has been buying Japanese stocks in the form of exchange-traded funds, with a goal of investing three trillion yen ($24.8 billion) in the Japanese market annually. Thus far the effort seems to be succeeding; the Nikkei index has gained nearly 15 percent year-to-date.