SINGAPORE, Nov 21 (Reuters) - Copper prices fell for a second session on Wednesday as trade tensions between the United States and China escalated ahead of an expected high-stakes meeting between the two nations next week. The United States administration on Tuesday said China has failed to alter its "unfair" practices, adding to tensions ahead of the meeting later this month between U.S. President Donald Trump and Chinese President Xi Jinping. All base metals contracts on the Shanghai Futures Exchange lost ground after turbulent trade on Tuesday with U.S. stocks and global oil market tumbling amid concerns over global economic growth. But the Shanghai market is expected to be subdued later this week due to a Thanksgiving holiday in the United States on Thursday and as investors stay on the sidelines ahead of the Trump-Xi talks, said analyst Helen Lau of Argonaut Securities. COPPER: London's three-month copper on the London Metal Exchange was down 0.1 percent at $6,176.5 a tonne by 0425 GMT, while Shanghai copper hit its lowest in nearly a week in early trade at 48,740 yuan ($7,018.71) a tonne. ZINC: Shanghai zinc lost 2.3 percent while London three-month zinc eased 0.3 percent, to be down 23 percent so far this year, Refinitiv Eikon data showed. Zinc fell on weaker Chinese automobile usage in October and a faster-than-expected rise in mined zinc supply, Argonaut's Lau said. ALUMINIUM: Global primary aluminium output rose to 5.414 million tonnes in October from 5.301 million tonnes in September, data from the International Aluminium Institute (IAI) showed on Tuesday. Shanghai aluminium touched its lowest since October 2016 in early trade of 13,625 yuan. MEXICO-US: Mexico expects Washington to begin lifting steel and aluminium tariffs against it later this month, when Canada, Mexico and the United States are slated to sign a revamped trade deal, the Mexican ambassador to the United States told McClatchy on Monday. WEAKER STEEL: Japan's top steelmaker Nippon Steel & Sumitomo Metal Corp is bracing for a weaker steel market in Asia because the escalating Sino-U.S. trade war may crimp steel demand in top buyer China and in Southeast Asia, a senior executive said.