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

       The Postal Service’s halt and reversal just hours later show how crucial parts of global delivery systems are grappling with sudden changes in U.S. trade policy, sowing confusion among businesses and potentially delaying shipments.

       On Saturday, Mr. Trump ordered that all Chinese imports would be subject to tariffs starting Tuesday. Until the change, parcels worth up to $800 apiece were not required to include detailed information about their contents and were not subject to levies. That was because they were allowed to take advantage of a provision, known as the de minimis exception, that many e-commerce companies have used to send goods to the United States from China without having to pay taxes on them.

       As of Wednesday, the Postal Service “will continue accepting all international inbound mail and packages from China and Hong Kong posts,” a spokesman for the service said. “The U.S.P.S. 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 these lower-value parcels a day, most of them from China, with little or no customs inspection and no duties collected.

       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 materials needed to make the drug. But many e-commerce companies have used the de minimis rule to bring regular consumer items from China into the United States without paying tariffs on them.

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