Nvidia late Tuesday notified regulators that it expects a $5.5 billion hit this quarter owing to a new US licensing requirement on the chip it can legally sell in the Asian country.

The company at the heart of helping to power artificial intelligence said it must obtain licenses to export its H20 chips to China because of concerns they may be used in supercomputers there.

President Donald Trump's decision over Nvidia is "signalling a tech-led decline for US equities" when Wall Street opens, noted Joshua Mahony, analyst at trading group Scope Markets.

After a relatively peaceful couple of days on markets following last week's tariff-fuelled ructions, investors were once again on the defensive, sending safe haven gold above $3,300 an ounce for the first time.

Nvidia shares tumbled around six percent in after-market trade, and its Asian suppliers were also hit.

Trump has also kicked off an investigation that could see tariffs imposed on critical minerals such as rare earths, which are used in a wide range of products including smartphones, wind turbines and electric vehicle motors.

"Nvidia dropped the mic, revealing fresh export curbs on AI gear headed to China," said Stephen Innes at SPI Asset Management.

"Then came the other shoe: Trump ordering a new probe into tariffs on critical minerals. Boom -- just like that, we're back in whiplash mode.

"Welcome to the new normal: one step forward, two tariff probes back," added Innes.

In Europe, London's benchmark FTSE 100 stocks index was down about 0.5 percent around midday, even as official data showed UK inflation slowed more than expected in March.

Paris and Frankfurt shed a similar amount.

The dollar slid once more against main rivals, helping gold to reach yet another fresh record high, this time at $3,317.75.

Oil prices rose nearly one percent after recent sharp falls on fears that the tariffs will dampen global economic growth.

However, cheaper oil could help put on lid on inflation, analysts said.

Trump's most recent moves mark the latest salvo in an increasingly nasty row that has seen Washington and Beijing hit each other with eye-watering tariffs.

China did little to soothe worries Wednesday by saying US levies were putting pressure on its economy, even if official data showed it expanded more than expected in the first quarter.

Beijing told Washington to "stop threatening and blackmailing".

A decision by Hong Kong's postal service to stop shipping US-bound goods in response to "bullying" levies added to the unease.

- Key figures around 1035 GMT -

London - FTSE 100: DOWN 0.4 percent at 8,220.27 points

Paris - CAC 40: DOWN 0.5 percent at 7,295.34

Frankfurt - DAX: DOWN 0.5 percent at 21,150.31

Tokyo - Nikkei 225: DOWN 1.0 percent at 33,920.40 (close)

Hong Kong - Hang Seng Index: DOWN 1.9 percent at 21,056.98 (close)

Shanghai - Composite: UP 0.3 percent at 3,276.00 (close)

New York - Dow: UP 0.4 percent at 40,368.96 (close)

Euro/dollar: UP at $1.1369 from $1.1291 on Tuesday

Pound/dollar: UP at $1.3272 from $1.3232

Dollar/yen: DOWN at 142.66 yen from 143.18 yen

Euro/pound: UP at 85.69 pence from 85.30 pence

Brent North Sea Crude: UP 0.9 percent at $65.23 per barrel

West Texas Intermediate: UP 0.9 percent at $61.87 per barrel

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