US customs agents have started collecting President Donald Trump's new 10 percent tariff on all imports from many countries, with higher levies on goods from 57 larger trading partners due to start next week. The initial tariff took effect at US seaports, airports, and customs warehouses, marking a rejection of the post-World War Two system of mutually agreed tariff rates. The tariffs are expected to evolve over time as countries negotiate lower rates. Trump's announcement caused global stock markets to plummet and wiped out $5 trillion in value for S&P 500 index companies.