Asian stocks swung on Wednesday after Nvidia's announcement of new US licensing rules on shipments of its new chip to China rattled investor confidence already shot by Donald Trump's sweeping trade war.

In Hong Kong, the benchmark Hang Seng Index ended down 1.91 percent at 21,056.98.

The Hang Seng China Enterprises Index fell 2.55 percent to end at 7,779.01, and the Hang Seng Tech Index fell 3.72 percent to end at 4,796.28.

After a relatively peaceful couple of days following last week's tariff-fuelled ructions, investors were once again on the defensive as a standoff between the world's top economic superpowers shows no signs of abating.

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

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

Chip behemoth Nvidia said on Tuesday that US officials had told the firm it must obtain licences to ship its new H20 semiconductors to China because of concerns they may be used in supercomputers there, adding the rule would last indefinitely.

The move marks the latest salvo in an increasingly nasty row that has seen Washington and Beijing hit each other with eye-watering tariffs, with the technology sector and security at the heart of the issue.

US levies on other trading partners – despite being mostly paused – have sent global markets into a tailspin as governments scramble to cushion themselves from the impact of the measures, with many heading to Washington for talks.

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

"Silence is never golden – it's just the calm before the next chaos cycle," said Stephen Innes at SPI Asset Management.

"And sure enough, the tape just got rattled again.

"Nvidia dropped the mic, revealing fresh export curbs on AI gear headed to China.

"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."

Tokyo, Sydney, Seoul, Taipei, Manila and Jakarta were also down.

Singapore, Mumbai, Bangkok and Wellington rose.

London fell even as UK inflation slowed more than expected in March, while Paris and Frankfurt also retreated.

A weak dollar, and an ongoing run into safe havens, saw gold spike to a fresh record high of US$3,291.81. (AFP/Xinhua)