Stocks are headed sharply lower at the open after Trump threatens more tariffs on China

U.S. stock futures plunged in after-market trading after President Donald Trump said he has asked the United States Trade Representative to consider $100 billion in additional tariffs against China.

In premarket trading Friday, the implied open for the Dow Jones industrial average was about 200 points lower, after sinking as much as 400 points Thursday evening. The implied open for the and Nasdaq were also deeply in the red.

Markets have been jittery in recent sessions amid fears of a potential trade war between the U.S. and China.

"In light of China's unfair retaliation, I have instructed the USTR to consider whether $100 billion of additional tariffs would be appropriate under section 301 and, if so, to identify the products upon which to impose such tariffs," Trump said in a Thursday statement.

U.S. stocks had finished higher on Thursday before the latest statement amid attempts by the Trump administration to talk down recent trade tensions. Still, concerns remained that the latest trade-related development could signal more uncertainty ahead.

"Markets rallied on the idea the tariffs were just to start a negotiation. Trump's $100 billion comment implies this is going to get a lot more serious and basically quasi-shatters the idea that the tariffs were just a negotiation starting point," Tom Essaye, founder of The Sevens Report, said.

Quincy Krosby, chief market strategist at Prudential Financial, added: "A pattern has developed for markets whereby tariff-related headlines can be strident only to be softened shortly afterwards by administration officials. In this instance, the president may be escalating the 'headlines' rather than seeking to escalate possibilities of a trade war."

Trump's comments come after China on Wednesday unveiled tariffs on up to $50 billion in American products annually. Beijing's list came after the U.S. drafted its own list of Chinese imports that would be targeted by proposed tariffs.

U.S. Trade Representative Robert Lighthizer called Thursday's proposed measures "an appropriate response to China's recent threat of new tariffs," but also added that additional tariffs would not be implemented until a public comment process was concluded.

— CNBC's Cheang Ming contributed reporting for this article.