Hongkong Post said it will "definitely not collect any... tariffs on behalf of the US and will suspend the acceptance of postal items containing goods destined to the US".

It added that it will stop accepting surface mail of US-bound items with immediate effect and air mail items starting from April 27.

Trump signed an order this month to scrap a duty-free exemption for small parcels from China, a rule that critics say aided the rise of Chinese-founded online retailers Shein and Temu.

The "de minimis" exemption allowed goods valued at $800 or under to enter the United States without paying duties or certain taxes.

Beijing and Washington have been locked in a fast-moving, high-stakes game of brinkmanship since the US president began his global tariff assault that has particularly targeted Chinese imports.

US duties on China are now at an eye-watering 145 percent, while Beijing has hit back with a 125 percent toll of its own on US imports.

Hong Kong, a free port with its own trade policies, has not followed China's lead in imposing retaliatory levies.

"The US is unreasonable, bullying and imposing tariffs abusively," the Hongkong Post said in its Wednesday statement.

"For sending items to the US, the public in Hong Kong should be prepared to pay exorbitant and unreasonable fees."

For US-bound surface mail parcels that have not yet been shipped, the service will contact the senders to return the items and refund postage starting April 22.

Postal items containing documents only will not be affected, it added.