Donald Trump's latest threat to impose an additional 100% tariff on Chinese goods is "a typical example of US double standards", China's government has said.

A commerce ministry spokesperson also said China could introduce its own unspecified "countermeasures" if the US president carries out his threat, adding it was "not afraid" of a possible trade war.

On Friday, Trump hit back at Beijing's move to tighten its rules for rare earths exports, accusing it of "becoming very hostile" and trying to hold the world "captive". He also threatened to pull out of a meeting with China's President Xi Jinping later this month.

But on Sunday, Trump wrote: "Don't worry about China, it will all be fine!"

"Highly respected President Xi just had a bad moment. He doesn't want Depression for his country, and neither do I. The U.S.A. wants to help China, not hurt it!!!" Trump said in a post on social media, without elaborating further.

Trump's comments on Friday rattled financial markets, with the S&P 500 share index closing down 2.7%, its steepest fall since April.

The president's words renewed fears of a trade war between the US and China.

In May, the two sides had agreed to drop triple-digit tariffs on each others' goods. which had raised the prospect of trade halting between the two countries.

This left US tariffs on Chinese goods facing an added 30% levy compared with the start of the year, while US goods entering China face a 10% tariff.

China's response - released by the commerce ministry in the form of written responses to journalist's questions - echoed language from the height of the recent trade conflict.

They criticised US export restrictions on chips and semi-conductors as well as defending China's own export controls on rare earths as "normal actions" to safeguard national security and that of all nations.

The spokesperson said that for "a long time", the US had "overstretched the concept of national security, abused export control measures" and "adopted discriminatory practices against China".

"Resorting to tariff threats is not the right way to engage with China," the spokesperson said.

"China's position on a tariff war has always been consistent: we do not want one, but we are not afraid of one."

Last week, China announced it was tightening export controls on rare earths and other materials critical for advanced tech manufacturing.

This was seen as key move, as the country processes about 90% of the world's rare earths, which are used in goods such as solar panels and smartphones.

The recent comments from Washington and Beijing are being seen by some as a means of strengthening positions ahead of future trade talks.

It is unclear whether a meeting between Trump and Xi, expected at a summit in South Korea later this month, will still proceed.