The market turmoil in China spread around the world, as global investors grew more anxious about the country’s currency and the health of its economy.

Chinese stocks plunged on Thursday, by more than 7 percent, forcing officials for the second time this week to halt trading for the day — in this case, after just 29 minutes.

The aftershocks carried over to Europe, where markets fell sharply once again. And futures trading indicated that Wall Street might open down by about 2 percent, after a sharp sell-off in the United States the day before.

The big question now is how much of the turmoil reflects rule changes and other policies at the Chinese stock market, where the first wave of sell-offs began last summer, and how much is based on broader economic fundamentals that might have a further impact on global growth.

Markets “are in a panic over what’s happening in China,” said Derek Halpenny, European head of global markets research at Bank of Tokyo-Mitsubishi UFJ in London. “People are saying, ‘Whoa, growth is way worse than we were expecting this year.’”

It has been a rocky start to the new year in global markets. The big fear is that China’s economy is slowing down, crimping global growth.

A downbeat Chinese manufacturing report first sent stocks spiraling on Monday, prompting the country’s market to close early. It also set off a global rout, with stocks in Europe and the United States getting hit.

China’s currency, the renminbi, continued to be a sore spot on Thursday, as the country’s central bank moved to help stabilize the situation.

The Chinese government, which closely controls the renminbi, has been allowing the value of the currency to decline steadily. It is a difficult process to manage, especially as companies and individuals send money out of the country at a rapid rate.

On Thursday morning before the stock market opened, China’s central bank set the rate for the renminbi at 6.5646 to the dollar, its lowest point in almost six years. When stock trading opened, investors dumped shares, once again shutting down the market.

The trick is preventing a gradual decline from turning into a rout.

Managing the currency is becoming harder for China. Investors, most of them domestic, are moving money out of the country before the buying power of the renminbi slides further.

China’s economy has also been steadily slowing, making it a less attractive place to invest. Fourth-quarter growth, which will be reported this month, is expected to be 6.9 percent, although some economists have expressed skepticism about the reliability of such figures.

The clearest indication of investor sentiment about the renminbi lies in the currency’s value in unrestricted trading here in Hong Kong. Traders have been selling renminbi in Hong Kong for a significantly lower price than the bottom of the government-authorized trading range in Shanghai.

The falling value of the renminbi in Hong Kong undermines confidence in the mainland’s currency. It then puts pressure on the central bank to keep pushing down the official trading range.

Taken together, the currency weakness, the economic slowdown and the stock market turmoil could force the government to take action. When stocks sold off last summer, China organized large-scale purchases by government-linked brokerages and investment funds.

Some of those measures may be adding to the current pain, though.

Under a new rule, trading stops for 15 minutes when losses hit 5 percent, a measure known as a circuit breaker. But the cooling-off period may be intensifying the sell-off.

Both times the circuit breaker was activated this week, the losses continued once trading resumed, taking stocks down 7 percent and forcing a stop in trading. On Thursday, trading was suspended after just 14 minutes. When it resumed 15 minutes later, the indexes almost immediately fell to the daily limit. Trading was then halted for the day.

Soon afterward, economic policy makers in China issued two statements meant to indicate that officials were taking matters in hand. First, the foreign exchange markets unit of the central bank said that “current conditions are supportive of a relatively stable” exchange rate. The comment was interpreted by some traders and economists as signaling that the central bank might intervene more heavily in currency markets to support the renminbi. There were indications that it had already begun to intervene more to prop up the renminbi in Hong Kong trading.

Subsequently, the China Securities Regulatory Commission announced that it was extending for three months a ban on stock sales by large shareholders. A previous ban, imposed in early July during a steep plunge in share prices at the time, had been scheduled to expire on Friday.

Erwin Sanft, the head of China strategy at Macquarie Group, based in Sydney, Australia, predicted further declines in Chinese stocks, but he said that the fall might not continue for long. “China is quite good at defensive measures,” he said.

The options for the government go far beyond the market.

To shore up the economy, China could further reduce interest rates so as to help the real estate market. It could also further increase its already considerable stimulus spending on infrastructure.

Still, while such measures might help in the short run, they would only add to one of China’s biggest problems in the long run: a huge overhang of debt that was used to finance poorly judged investments. Many of those investments, like high-speed rail lines built in smaller provincial capitals for political reasons, may struggle to generate enough of an economic return to cover the interest on the money that was borrowed to finance them.

“The more you try to alleviate, the worse it gets in the long term,” said Viktor Shvets, the head of Asian strategy at Macquarie.

As for the broader effects of China’s problems, Mr. Halpenny, the London analyst, said, “There has to be a point when the market sensitivity to Chinese devaluations declines.”

“We don’t expect this degree of volatility to continue,” Mr. Halpenny said. “But it looks like it’s going to be an interesting year.”