Neither Shein or Temu immediately responded to BBC requests for comment.
The duty-free rule was closed by the Trump administration earlier this month.
Some shoppers told the BBC that they rushed through purchases ahead of that deadline.
The latest rates came after the US and China released a joint statement announcing they would temporarily reduce their tit-for-tat tariffs and start a new round of trade negotiations.
Share markets jumped on Monday after Trump said weekend talks had resulted in a “total reset” in trade terms between the two countries, a move that went some way to ease concerns about a trade war between the two countries.
Under the agreement, the US will lower those tariffs from 145% to 30%, while China’s retaliatory tariffs on US goods will drop to 10% from 125%.
Trump told reporters, that, as some of the levies have been suspended rather than cancelled altogether, they might rise again in three months time, if no further progress was made.
But the president said he did not expect them to return to the previous 145% peak.
“We’re not looking to hurt China,” Trump said after the agreement was announced, adding that China was “being hurt very badly”.
Trump added that he expected to speak to Chinese President Xi Jinping “maybe at the end of the week”.
