The U.S. imposed an additional 50% tariff on Chinese imports on Wednesday afternoon, triggering sharp selloffs in global financial markets and forcing South Korea into emergency response mode. The tariff, which took effect at 12:01 a.m. EDT (1:01 p.m. KST), is the most severe in over a century and forms the centerpiece of U.S. President Donald Trump’s “America First” trade doctrine. China responded Wednesday evening by announcing it would raise tariffs on select U.S. imports from 34% to 84%, effective April 10. Concurrently, the European Commission also announced that EU Member States had unanimously approved trade countermeasures against the U.S. in response to American steel and aluminum tariffs. The duties are set to take effect on April 15.

South Korea, meanwhile, is facing a 26% U.S. tariff on its exports. The trade ministry responded by unveiling an emergency relief package that includes liquidity support, tax deferrals and expanded export insurance for affected small and mid-sized suppliers. Acting President Han Duck-soo held a 30-minute call with Trump on Tuesday, urging cooperation. He later told CNN that South Korea would not pursue retaliatory tariffs, saying tit-for-tat escalation “would not improve the situation.”