Billionaire Trump backer warns of 'economic nuclear winter' over tariffs

A billionaire backer of Donald Trump has urged the US president to pause his recently announced trade tariffs, or risk "a self-induced, economic nuclear winter".

Amid market turmoil, hedge fund manager Bill Ackman said the president should take three months to allow countries to renegotiate their trading relationships with the US.

On Monday, Mr Ackman's warning was echoed by other prominent Wall Street figures, with JPMorgan Chase chairman Jamie Dimon saying that Trump's tariffs risked pushing up prices for Americans.

Despite the shockwaves, the American president is moving ahead, with the White House rushing to label a rumour he might put new tariffs on pause as "fake news".

The rumour on Monday morning that Trump was considering a 90-day pause briefly lifted a swiftly sinking stock market after it was reported on financial network CNBC.

The White House almost immediately shot down the report, showing Trump's commitment to his new import taxes. Stock prices largely stabilised afterward.

The "baseline" tariffs of 10% on most country's goods that Trump announced last week have already gone into effect, while the higher "reciprocal" rates he wants to impose on the "worst offenders" are expected later this week. Some countries are seeking to negotiate lower rates with the White House.

The new tariffs, added to steep levies Trump has already put on goods from Canada and Mexico, as well as all automobile imports, are worrying business and economic leaders that they will push up prices for American consumers and spark a global trade war.

The head of BlackRock, the world's largest asset manager, said on Monday that the tariffs will raise prices and possibly inflation, and contribute to an economic downturn, according to media reports.