Investors bought dollars, sold stocks and fretted about inflation on Monday in a scramble to assess the risk of a trade war after Donald Trump put tariffs on top US trading partners.

Trump's orders for additional levies of 25 percent on imports from Mexico and most goods from Canada, as well as 10 percent on goods from China are light on detail.

But they kick in on Tuesday and have jolted markets that had assumed Trump was mostly bluff and bluster.

The selloff extended beyond just Canadian and Mexican markets and stocks directly in the line of fire, to cryptocurrencies, stocks and even the safe-haven Japanese yen, as investors tried to second-guess the volatile president's next moves.

Worries about the hit to growth from the inflationary impact of the wide-ranging tariffs and the uncertainty that creates for the Federal Reserve played a part, causing everything but the dollar and long-term US Treasuries to be sold.

"Trump's trade war has started," said Alvin Tan, head of Asia currency strategy at RBC Capital Markets in Singapore, noting it was hard to see the US dollar retreating any time soon.

The dollar has been the main mover, gaining as Trump headed for and then won office because investors figured tariff-hit countries would weaken their currencies to offset the impact.

On Monday, the euro fell 1.3 percent on fears Europe may be next on the tariff list.

Canada's dollar skidded to a 20-year low on the greenback, China's yuan slid in offshore trade, oil jumped, metals slumped and US equity futures dropped about two percent on risks to US companies' bottom lines.

Trump said the tariffs may cause "short term" pain for Americans, and while he would speak on Monday with the leaders of Canada and Mexico, which have announced retaliatory tariffs of their own, he downplayed expectations that they would change his mind.

Analysts said equity bulls are re-evaluating their Trump trades.

"Equity bulls seduced by 'Trump is good for equities' narrative are subject to a rude wake-up call from the potentially jarring impact on growth/earnings amid retaliatory tariff spirals," Mizuho said.

Shares in Hong Kong, Tokyo, Sydney, Seoul and Taipei made losses around two percent in the morning.

European stock futures slid 2.8 percent.

Trump has linked the tariffs to the flow of migrants and drugs - particularly fentanyl - into the US and demanded crackdowns in Canada, China and Mexico.

China and Mexico have said fentanyl is America's problem, so prospects of a breakthrough are unclear.

Beijing said it would challenge Trump's tariffs at the World Trade Organisation and take unspecified countermeasures. (Reuters)