HONG KONG - Shares in Asian-listed commodity firms fell on Tuesday, after a plunge in trader Glencore PLC stock a day earlier unnerved resource sector investors already worried about weak demand from China. Glencore’s London-listed shares tumbled 30 percent on Monday after analysts at investment bank Investec raised doubts about its valuation if spot metal prices do not improve. The note also pointed to high debt levels and a need for deeper restructuring. In Singapore, shares in commodity trader Noble Group fell as much as 15 percent to their lowest since late 2008. Miner BHP Billiton dropped 6 percent to its lowest since December 2008, and smaller rival Rio Tinto Ltd lost 4.5 percent to its lowest since May 2009. “There is a crisis of confidence and people are continuing to de-leverage commodity stocks exposure,” said Benjamin Chang, CEO of hedge fund LBN Advisers, which manages about $600 million in funds. “People are ignoring valuations as the near-term outlook continues to be bearish,” he added. London copper held steady on Tuesday but was near last month’s six-year trough as concerns about weak demand from China hammered mining equities and eroded support for metals.