In a rapid escalation of the trade conflict between the world‘s two economies, President Donald Trump threatened to impose a 10 percent tariff on $200 billion Chinese goods.

Trump’s latest move, as Washington fights trade battles on several fronts, was unexpectedly swift and sharp.

It was retaliation, he said, for China’s decision to raise tariffs on $50 billion in U.S. goods, which came after Trump announced similar tariffs on Chinese goods on Friday.

“After the legal process is complete, these tariffs will go into effect if China refuses to change its practices, and also if it insists on going forward with the new tariffs that it has recently announced,” Trump said in a statement on Monday.

The comments sent global stock markets skidding and weakened both the dollar and the Chinese yuan on Tuesday. Shanghai stocks plunged to two-year lows.