The selling looks to continue on Friday morning as equity futures are pointing to further declines.
Dow Industrial futures are 0.2 percent lower, S&P 500 futures are slipping by 0.3 percent and Nasdaq futuers are off 0.6 percent.
The Dow Jones Industrial Average had been up 311 points before the tweet -- meaning that within minutes of the tariff news the blue-chip index had plunged from a peak to a trough of more than 600 points.
The market's gains before the tariff news stemmed from optimism that the Federal Reserve would cut interest rates again in September.
News of the additional tariffs follows the latest round of trade negotiations between the U.S. and China. The next meeting will be in September.
The sudden risk-off sentiment was reflected in the yield of the 10-year Treasury, which tumbled to 1.87 percent, its lowest level since November 2016. Bond yields and bond prices move in the opposite direction.
Equities started the day higher, rebounding from Wednesday's selling spurred on by the Federal Reserve cutting interest rates for the first time in a decade and comments by the Fed Chair.
|I:DJI||DOW JONES AVERAGES||30891.04||-76.78||-0.25%|
|I:COMP||NASDAQ COMPOSITE INDEX||11327.542659||+5.31||+0.05%|
Chairman Jerome Powell suggested Wednesday that the cut wasn't the beginning of a long easing cycle. He also reiterated that the central bank would continue monitoring incoming economic data. That helped send the Dow to a loss of 333 points or 1.2 percent.
On the economic calendar, weekly jobless claims came in at 215,000, slightly higher than expected. On Wednesday, ADP reported the private sector added 156,000 jobs in July. This comes ahead of Friday's monthly employment report. Economists estimate that 164,000 workers were added to payrolls.
Technology and consumer stocks were among Thursday's movers.
|IBM||INTERNATIONAL BUSINESS MACHINES CORP.||137.62||-3.50||-2.48%|
|HD||THE HOME DEPOT INC.||283.73||+4.65||+1.67%|
General Motors shares moved higher on better-than-expected net profit boosted by pickup trucks, SUVs and crossover sales.
Yum Brands beat expectations for quarterly profit helped by better-than-expected growth at all of the restaurant operator's chains, including Pizza Hut. s Shares traded to a record high. Excluding items, the company earned 93 cents per share, beating expectations. Total revenue of $1.31 billion also beat estimates.
|GM||GENERAL MOTORS CO.||32.37||+0.18||+0.56%|
|YUM||YUM! BRANDS INC.||117.33||+0.62||+0.53%|
|VZ||VERIZON COMMUNICATIONS INC.||51.42||-0.22||-0.43%|
Verizon Communications rose after the wireless carrier beat quarterly profit estimates.
Crude oil plunged nearly 8 percent, or $4.64, to $53.94 per barrel -- the commodity's biggest price plunge since Feb. 4, 2015.
That drop hammered shares of oil producers.
|XOM||EXXON MOBIL CORP.||84.81||-2.74||-3.13%|