Trump lashes out at China, vows quick response

US President Donald Trump lashed out at Beijing and vowed a quick response to China's plans for new tariffs, while ordering American companies to leave the country.

The blistering Twitter screed called into doubt chances for a quick resolution to the escalating trade war between the world's economic superpowers, which by the end of the year will cover nearly all imports and exports exchanged between the two countries.

"We don't need China and, frankly, would be far... better off without them, Trump said.

The trade friction already has slowed US growth, and undercut the global economy, so the threat of a deterioration sent stock markets falling sharply.

The Dow lost more than 500 points from its peak, while London's FTSE and the German DAX also lost ground.

"Our Country has lost, stupidly, Trillions of Dollars with China over many years. They have stolen our Intellectual Property at a rate of Hundreds of Billions of Dollars a year, & they want to continue. I won't let that happen!," Trump wrote.

"Our great American companies are hereby ordered to immediately start looking for an alternative to China, including bringing... your companies HOME and making your products in the USA."