Worries about the health of China’s economy shook markets again Friday, hitting stocks in Asia and Europe.

Signs of a sharp slowdown in the world’s second-largest economy have rattled investors since Beijing surprised markets last week by devaluing its currency.

On Friday, an early gauge of China’s factory activity fell to a six-and-a-half year low in August, heaping further pressure on beleaguered stocks and commodities.

The Shanghai Composite Index tumbled 4.3%, hitting its lowest level since March despite Beijing’s efforts to prop up the market in recent weeks. In Japan, the Nikkei fell 2.6% to a six-week low.

“It becomes ever more evident that China’s economy is cooling off,” said Jeroen Blokland, a portfolio manager at Robeco, which manages $307 billion of assets.

In Europe, the Stoxx Europe 600 was 0.7 percent lower late morning, on course for its biggest weekly loss since December.

European markets picked up slightly from deeper opening losses as business activity data for the eurozone showed a quickening pace of expansion in August.

The moves follow a global selloff on Thursday, which sent the Dow Industrials to its lowest level since October. Some investors and analysts say they think the tumult in markets could complicate the Federal Reserve’s plans to raise interest rates.

U.S. stock futures indicated a 0.1 percent opening loss for the Dow and the S&P 500. Changes in futures aren’t necessarily reflected in market moves after the opening bell.

"The Chinese have created an air of fragility around the globe. Markets will now surely have to firm up considerably for the Fed to pull the trigger next month," said Deutsche Bank analyst Jim Reid.

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