American customs officials began collecting the new 10% tariff on imports from many countries on Saturday morning after the US stock market saw its worst week since 2020 in response to President Trump's 'Liberation Day' tariff announcement that on Wednesday.

"This is the single biggest trade action of our lifetime," Kelly Ann Shaw, a trade lawyer and former White House trade adviser during Trump's first term, told Reuters. Shaw added that while she expected the tariffs to evolve through negotiations, the new policy is "a pretty seismic and significant shift in the way that we trade with every country on earth."

Reuters reported that countries initially hit with the 10% tariff after midnight on Saturday included Australia, Britain, Colombia, Argentina, Egypt, and Saudi Arabia.

Elon Musk, appearing at an event on Saturday, said that "Europe and the United States should move, ideally, in my view, to a zero-tariff situation."

Additional duties on goods from 185 countries, whom Trump described as the "worst offenders" in terms of perceived unfairness on trade, are slated to start on Wednesday, April 9. The tariff rate applied to the European Union under the policy is 20%.

Various countries are still deciding how to respond (or not), and companies have begun adjusting to the new reality — largely by raising prices. Some countries responded with new tariffs of their own: Canada announced new duties on certain vehicles imported from the US, and China announced that it will impose countermeasures against the US starting April 10, including a 34% tariff on US goods.