Australian shares fell from near-record highs as copper prices plunged after a surprise tariff decision by the United States. The mining sector led the decline, with major companies like BHP, Rio Tinto, and Sandfire Resources experiencing significant losses. The tariff, which only applies to semi-finished copper products, caused an unwinding of bets that had driven up copper prices, resulting in the metal's largest one-day drop. Other sectors were also affected, with Cettire and Flight Centre seeing sharp declines due to new US trade measures and challenging market conditions. Despite the broader downturn, the major banks managed to post modest gains.