US customs agents began collecting a new 10% tariff on imports from numerous countries on Saturday, marking a dramatic shift in American trade policy under former President Donald Trump.

The baseline tariff, effective from 12:01 a.m. ET, impacts goods entering via seaports, airports and customs warehouses. Starting Wednesday, higher levies—ranging from 11% to 50%—will target 57 major trading partners, including a 20% tariff on EU goods and 34% on Chinese imports.

“This is the single biggest trade action of our lifetime,” said Kelly Ann Shaw, former White House trade adviser. Speaking at the Brookings Institution, Shaw described the move as a “seismic” departure from decades of mutually agreed tariffs.

The announcement triggered turmoil in global markets, erasing $5 trillion in value from S&P 500 firms by Friday. Oil and commodity prices fell sharply while investors rushed to safe-haven assets.

Countries immediately affected include Australia, Britain, Egypt, and Saudi Arabia. However, goods already in transit before the Saturday deadline have until May 27 to arrive tariff-free.

Canada and Mexico remain exempt under existing 25% fentanyl-related duties. Additionally, over 1,000 product categories—including energy imports, pharmaceuticals, and semiconductors—were excluded from the new tariffs, covering $645 billion in 2024 imports.

Vietnam, facing a 46% tariff, agreed Friday to begin talks with the US.