President Donald Trump on Friday threatened to cancel a meeting with Chinese President Xi Jinping next week and impose new tariffs on China, in what's amounting to a fresh spike in trade tensions between Washington and Beijing.

Trump was scheduled to meet Xi later this month on the sidelines of the Asia-Pacific Economic Cooperation Summit in South Korea. Now its uncertain whether that leg of his foreign trip will materialize as planned.

"I was to meet President Xi in two weeks, at APEC, in South Korea, but now there seems to be no reason to do so,” Trump posted on social media.

Trump cited a new Chinese restriction on rare-earth exports that make up critical components in smartphones, military hardware, autos, and more. Then he threatened new tariffs on Chinese goods without specifying which ones.

“One of the Policies that we are calculating at this moment is a massive increase of Tariffs on Chinese products coming into the United States of America,” Trump said, adding "many other countermeasures" are under "serious consideration.”

The White House did not immediately respond to a request for comment.

Financial markets plunged following Trump's caustic comments on China. The Dow Jones initially dropped over 500 points before recouping some of those losses at around 12pm ET. The S&P 500 followed a similar trajectory and had shaved off about 100 points, or 1.5%, until starting to climb again.

Shares in rare-earth producers jumped early Friday afternoon. MP Materials surged 11 points, or 15%. The Trump administration took a 15% stake in the company in July.

For its part, Beijing said the latest clampdown on rare-earth exports was meant to strengthen its national security. Analysts, though, believed the Chinese government was attempting to gain the upper hand in ongoing trade negotiations between the two largest economies.

The Chinese government enacted and later removed identical rare-earth export restrictions in May as part of an interim accord that lowered trade tensions. The U.S. and China still maintain double-digit tariffs imposed on much of each other's products.

On Friday, Beijing separately announced that a new fee will be charged on American vessels docking in Chinese ports starting Oct. 14. It will amount to 400 yuan per net ton, or $56.

The Department of Commerce did not immediately respond to a request for comment. Earlier this year, the Trump administration announced a similar fee — on Chinese ships docking in the U.S., totaling $50 per net ton — that takes effect on the same day.