US tariffs serious violation, will take countermeasures: China

China warned on Friday it will take "countermeasures" if the United States follows through on its threat to impose tariffs on $300 billion in Chinese goods in an escalation of their trade war.

The commerce ministry said in a statement that President Donald Trump's move to impose the new tariffs on September 1 was a "serious violation" of a truce that was reached with Chinese leader Xi Jinping in June.

It did not specify what kind of countermeasures it would take, but in the past China has hinted that it could restrict exports of rare earths that are vital to the US technology industry, and it is also drawing up a blacklist of "unreliable" foreign companies.

Earlier, China's foreign minister had said tariffs were "not a constructive" way to solve the US trade war after President Donald Trump threatened to hit $300 billion worth of Chinese goods with new duties.

"Slapping on tariffs is definitely not a constructive way to resolve economic and trade frictions, it's not the correct way," Wang Yi said on the sidelines of a meeting of Southeast Asia's top diplomats in Bangkok, according to footage broadcast on a Chinese television station.

US President Donald Trump had announced on Thursday he will hit China with punitive tariffs on another $300 billion in goods, prompting Beijing to warn it was the wrong way to resolve the trade war.

The sudden deterioration meant the world's two largest economies have now erected trade barriers covering virtually all of their $660 billion in annual trade in merchandise - confirming economists' fears and sending shudders through Wall Street.

The 10 per cent duties will take effect September 1, and come on top of the 25 per cent tariffs on $250 billion in imports already in place.

He later raised the possibility he could increase the duties further.