The Dow Jones Industrial Average reacted harshly to a big drop in Chinese stocks overnight, falling over 450 points on Monday, more than 2.5 percent, in mid-morning trading.

Wall Street is again reacting to poor numbers in China, USA Today reports. Chinese stocks fell more than 7 percent overnight, which forced authorities to halt trading before the actual closing time.

Chinese manufacturing numbers were weaker than expected, signaling a contraction for the fifth straight month in China, the world's second biggest economy.

China had its worst start of the year, according to Bloomberg. In the U.S., it was the worst start of the year for the Dow in 84 years.

Last year, China initiated a "circuit breaker" rule to slow down markets and ease panic when stocks fall by 5 percent or more. The precaution was put to use in mid-afternoon trading to halt the CSI 300 index for 15 minutes. When trading resumed, stocks continued to fall by more than 7 percent, causing the Chinese market to close for the day early.

Investors then saw U.S. manufacturing numbers fall, which added to fears of a global economic slowdown. An index of U.S. factory activity fell from 48.6 to 48.2, the Institute for Supply Management reported on Monday. That reading is the lowest since June 2009.

Tensions in the Middle East between Saudi Arabia and Iran have also increased investor concerns. The two countries severed ties on Sunday.

The world's markets all responded with falling stocks. Asian markets in China, Hong Kong and Japan all fell. European markets followed Asia, with Germany and France's markets falling as well.

Just like last year, Wall Street is closely monitoring China. Signs of a slowdown in China are usually a signal that stocks will fall globally.

"A lot of it has to do with China and a lot of it is overdone," Art Hogan, chief market strategist at Wunderlich Securities, told CNBC. "The China PMI hasn't changed much. It's not unusual to have an outsized reaction when you've got a base case that 2016 could be a tough year."

He added, "I think it's very much global markets are in a risk-off mode. It's very hard to step in the way of [that]."