US President Donald Trump doubled down on his blanket tariffs on Monday as he threatened to escalate trade tensions with China in the midst of global stock market turmoil and mounting investor anxiety.

As markets reeled from another volatile day of trading, Trump used his Truth Social platform to give Beijing a Tuesday deadline to withdraw its retaliatory tariffs of 34%.

He warned that failure to comply would trigger fresh US duties starting Wednesday: "ADDITIONAL Tariffs on China of 50%."

China had announced plans to impose a 34% tariff on US imports starting Thursday, in direct retaliation for a matching 34% duty on Chinese goods unveiled by the US president last week.

Total US tariffs on Chinese imports are set to rise to 54%, factoring in a previously imposed 20% toll, and they could now increase even further.

Also last week, the US government announced universal levies of a minimum of 10% on imports from almost all its trading partners - with increased tariffs for individual countries or trading blocs.

When asked by a reporter at the White House if he would pause tariffs to allow for negotiations, Trump replied: "We're not looking at that."

In Brussels, the European Union is continuing in its endeavour to de-escalate.

The EU offered the United States an agreement on "zero-for-zero tariffs for industrial goods," European Commission President Ursula von der Leyen announced, two days before 20% tariffs on EU exports enter into force.

"Europe is always ready for a good deal, so we keep it on the table," von der Leyen told reporters.

However, von der Leyen said that while the EU remains committed to negotiating with the US, it is also preparing potential countermeasures should talks break down.

The issue was a key topic during meetings between EU trade ministers and their advisers in Luxembourg on Monday.

The White House has meanwhile denied speculation about a possible suspension of the massive US tariff package. A government official described the rumours as "fake news" when asked for comment.

The speculation about a pause had caused a stir on social media and led to significant market fluctuations.

The rumours may have been triggered by an X post over the weekend by hedge fund billionaire Bill Ackman, who had previously supported Trump.

On Sunday, Ackman suggested a 90-day pause to renegotiate "unfair asymmetric tariff deals" and attract new investments worth trillions of dollars to the US.

He described the new tariffs planned for Wednesday against nearly all countries as an "economic nuclear war."

World markets declined once again on Monday as investors remained convinced that the US government will stick to its hefty tariffs despite some signs that Washington is willing to negotiate.

New York's Dow Jones Industrial Average fell 3.3% at the start of trading, but recovered to close down 0.9%.

The Nasdaq 100, which is predominantly composed of technology stocks, dropped more sharply at the opening, with a 3.5% decline but closed with a small gain of almost 0.2%.

Investors appear particular wary of Trump comparing the tariffs to medicine over the weekend.

Germany's leading stock market index, the DAX, closed down 4.13% to 19,789.62 points, having plummeted 10% in early trading.

European stocks plunged sharply at the open and, despite a brief recovery, ended the session significantly lower.

Several major indices hit multi-month lows as investor sentiment remained overwhelmingly negative.

"I don't want anything to go down, but sometimes you have to take medicine to fix something," Trump had said.

Trump's blanket minimum 10% tariff on imports from all countries took effect on Saturday, with the even steeper tariffs set to take effect on Wednesday for nations with which the US has higher trade deficits.

If the US tariffs stay in place, key trading partners, such as the EU and China, will respond with retaliatory tariffs, most experts believe, and this would in turn stifle the global economy.

Trump, in a flurry of posts on his Truth Social network, acknowledged that "countries from all over the World are talking to us. Tough but fair parameters are being set."

He said he spoke with Japanese Prime Minister Shigeru Ishiba on Monday and Ishiba is "sending a top team to negotiate!"

But he said Japan has "treated the U.S. very poorly on Trade" and added that Japan doesn't "take our cars, but we take MILLIONS of theirs," noting that agriculture and many other items are at issue.

"It all has to change, but especially with CHINA!!!"

Economists are worried about how the tariff spat will affect inflation and the US Federal Reserve's interest rate policy is therefore seen as unclear.