Equities have been battered leading up to the US president's announcement -- which he has dubbed "Liberation Day" -- with warnings that friend and foe are in the crosshairs after what he says is years of "ripping off" the United States.

He has trailed the measures for weeks, initially suggesting they would match whatever levies other countries impose.

But US media reported he has also considered either blanket 20 percent levies or another plan where some countries get preferential treatment.

Sweeping auto tariffs of 25 percent announced last week are also due to come into effect on Thursday.

The White House has said Trump will unveil his decision at 4:00 pm in Washington (2000 GMT), after Wall Street markets close, with the Republican promising a new "golden age" of US industry.

However, officials admitted he was still ironing out the details late Tuesday.

Analysts said the ongoing uncertainty was spooking markets.

"Investors and company management dislike uncertainty, and the piecemeal, unreliable way in which tariff announcements are being delivered is creating plenty of it," said Oliver Blackbourn and Adam Hetts at Janus Henderson Investments in a commentary.

"Estimates on what the average tariff rate will look like range from a few percentage points in moderate outcomes to double-digit levels in more forceful scenarios," they added.

"What does seem less uncertain is that tariffs are, without much exception, likely to be bad for economic growth, consumers, and markets."

Pepperstone Group's Chris Weston said the suggestion that the tariffs would be effective immediately would provide some sort of certainty, even if it limited the scope for talks.

"This scenario -- while hardly a positive for economics or earnings assumptions -- would increase the conviction behind how we respond to the 'facts'," he explained.

"That said, life is never straightforward, and we will still need to consider the counter response from other countries."

The planned duties have ramped up fears of a global trade war after several countries warned they were lining up their responses.

With that in mind, economists have warned that economic growth could take a hit and inflation reignite, dealing a blow to hopes that central banks would continue cutting interest rates.

Asian markets skittered between gains and losses through the day.

Tokyo, Shanghai, Sydney, Wellington, Taipei, Manila, Mumbai and Bangkok rose, while Singapore, Seoul slipped with London, Paris and Frankfurt. Hong Kong barely moved.

Safe haven gold held above $3,100 after touching a record high $3,149.00 on Tuesday.

HSBC strategists led by Max Kettner warned Wednesday might not mark the end of the tariff uncertainty.

"We'd argue the potential is in fact higher for the 2 April deadline to introduce even more uncertainty -- and hence prolonged broad-based weakness in leading indicators," they said.

Chinese tech giant Xiaomi dropped three percent in Hong Kong, extending Tuesday's fall of more than five percent after the firm confirmed one of its electric vehicles was involved in an accident in China that left three people dead.

- Key figures around 0815 GMT -

Tokyo - Nikkei 225: UP 0.3 percent at 35,725.87 (close)

Hong Kong - Hang Seng Index: FLAT at 23,202.53 (close)

Shanghai - Composite: UP 0.1 percent at 3,350.13 (close)

London - FTSE 100: DOWN 0.5 percent at 8,596.26

Euro/dollar: DOWN at $1.0792 from $1.0793 on Tuesday

Pound/dollar: DOWN at $1.2912 from $1.2920

Dollar/yen: UP at 149.64 yen from 149.53 yen

Euro/pound: UP at 83.58 pence from 83.51 pence

West Texas Intermediate: DOWN 0.7 percent at $70.73 per barrel

Brent North Sea Crude: DOWN 0.6 percent at $74.01 per barrel

New York - Dow: FLAT at 41,989.96 (close)

dan/fox

HSBC

Xiaomi