China said it would never accept the "blackmail nature" of the United States after Washington escalated tariff threats against the nation, the Ministry of Commerce said on Tuesday.

The US threats were "a mistake on top of a mistake", a ministry spokesperson said in a statement, urging the US to properly resolve differences with China through dialogue with mutual respect and on an equal footing.

Trump has threatened to impose an additional 50 percent duty on US imports from China on Wednesday if Beijing did not withdraw the 34 percent tariffs it had slapped on US products last week. Those tariffs had come in response to 34 percent "reciprocal" duties announced by Trump.

China's retaliatory levies are the firmest response yet to Trump's announcement, which has been met with bewildered condemnation from other leaders.

Overnight, Liu Pengyu, spokesman for Beijing's embassy in the United States, said China would not cave to pressure or threats.

"We have stressed more than once that pressuring or threatening China is not a right way to engage with us. China will firmly safeguard its legitimate rights and interests," said Liu.

He described Trump's threat as a "typical move of unilateralism, protectionism and economic bullying."

Stocks in mainland China and Hong Kong cratered on Monday as part of a worldwide stocks rout in response to Trump's tariffs. The Hang Seng Index recorded its biggest drop since the 1997 Asian financial crisis, falling 13.2 percent. (Agencies)