The stock market fell sharply Friday, after China announced it would slap retaliatory tariffs on $75 billion worth of U.S. goods and President Donald Trump vowed to fight back.

The Dow Jones Industrial Average fell by more than 621 points, a dip of about 2.37 percent, after a series of tit-for-tat tweets by the president that ordered American companies to find alternatives to China. The Nasdaq Composite and S&P 500 tumbled by 3 percent and 2.59 percent, respectively.

Markets had been higher earlier in the day, ahead of a speech by Federal Reserve Chairman Jerome Powell, who has been repeatedly lambasted by Trump for not lowering rates more readily. Wall Street, which has reacted with increasing volatility to any nuance in Powell's speeches, leveled out after the chairman's prepared remarks indicated the nation's central bank would continue to "act as appropriate" to maintain the economic expansion.

Meanwhile Friday, Trump savaged Powell as an "enemy" who could be worse for the United States than Chinese President Xi Jinping.

“As usual, the Fed did NOTHING! It is incredible that they can ‘speak’ without knowing or asking what I am doing, which will be announced shortly,” Trump tweeted. “We have a very strong dollar and a very weak Fed. I will work ‘brilliantly’ with both, and the U.S. will do great.”

Trump added: “My only question is, who is our bigger enemy, Jay Powell or Chairman Xi?” referring to the Chinese leader. Trump misspelled Powell's name in an initial tweet, which he then deleted.

Starting Sept. 1, tariffs of 5 percent will be imposed upon soybeans and crude oil, with the second tranche of products taxed at 10 percent beginning Dec. 15, according to a statement from the Chinese Ministry of Commerce. American cars will be taxed at 25 percent, also beginning in mid-December.

“If the U.S. obstinately clings to its own way, China has no choice but to take corresponding countermeasures,” a Ministry of Commerce spokesman warned Thursday.

Earlier this month, Trump made good on his threat to impose 10 tariffs on the remaining $300 billion of Chinese goods imported to the U.S.

The trade war between China and the U.S., the world's two largest economies, has rocked markets across the world for the last year and a half and contributed to a global economic slowdown that some economists believe could trigger a recession.