The United States Postal Service on Wednesday said it would continue to accept packages from China and Hong Kong, reversing a decision to temporarily halt those deliveries after an order by President Trump took effect that ended duty-free handling of many smaller parcels.

Mr. Trump ordered on Saturday that all goods leaving China starting on Tuesday must follow the rules for higher-value shipments. Until the change, parcels worth up to $800 apiece were not required to include detailed information on their contents and were not subject to tariffs.

A spokesman for the postal service said that as of Wednesday, it “will continue accepting all international inbound mail and packages from China and Hong Kong Posts. The USPS and Customs and Border Protection are working closely together to implement an efficient collection mechanism for the new China tariffs to ensure the least disruption to package delivery.”

The United States imports close to four million of such lower-value parcels a day with little or no customs inspection and no duties collected, with most of them coming from China.

The Trump administration and other critics have contended that allowing these packages into the United States has created a conduit for fentanyl, a synthetic opioid, and related supplies to enter the United States.

But the duty-free provision on lower-value parcels, known as the de minimis rule, has also been used by many e-commerce companies to bring regular consumer items from China into the United States without paying tariffs on them.