Stock markets fell around the world on Monday following a rout in Chinese shares after weak manufacturing data in the world’s second-largest economy sparked fears of a global economic slowdown.

News that US factory activity slowed in December and tensions between Saudi Arabia and Iran increased trader concerns.

China’s CSI 300 Index of large stocks listed in Shenzen and Shanghai fell 7%, a rout that triggered a circuit-breaker that halted trading. Hong Kong’s Hang Seng China Enterprises Index fell 3.6%.

The Stoxx Europe 600 Index fell 2.5 %, Germany’s DAX Index slid 4.3%, and the MSCI Emerging Markets Index fell 3.3%.

In New York, the Nasdaq and the S&P 500 had their worst start to a year since 2001, according to Reuters data.

The S&P 500 fell 1.53 percent, the Dow Jones industrial average fell 1.58%, and the Nasdaq tumbled 2%.

“The China 7-percent drop last night and the close of the market, along with Saudi Arabia, are causing investors to rethink to their growth estimates and the geopolitical risk that’s really out there,” Paul Mendelsohn, chief investment strategist at Windham Financial Services, told Reuters.