BEIJING, Oct 22 (Reuters) - London copper prices rose for a second session on Monday, extending a rally fuelled by a pledge from China's central bank that it would support firms with liquidity problems. The pledge was followed by comments from Chinese President Xi Jinping on Sunday that the ruling Communist Party would always support private-sector firms. China is "multiplying its efforts to support the economy, and in particular, the infrastructure sector amid domestic and international headwinds," such as the trade war with the United States and high debt levels, Fitch Solutions said in a note. The country's demand for copper, an economic bellwether, "will improve over the coming months as property completions and grid investment picks up and demand from the autos and consumer sectors remain buoyant," added the research house. FUNDAMENTALS: * LME COPPER: Three-month copper on the London Metal Exchange was up 0.8 percent at $6,270.50 a tonne, as of 0418 GMT, extending a 1 percent jump from the previous session. * SHFE COPPER: The most-traded December copper contract on the Shanghai Futures Exchange climbed 1 percent to 50,470 yuan ($7,282.09) a tonne by the mid-session interval. * COPPER PREMIUMS: China's copper import premiums SMM-CUYP-CN are at $117.50 a tonne, just below the recent three-year high of $120 a tonne, indicating strong demand for physical metal. * OTHER METALS: Nickel, used to make stainless steel, was the biggest climber, tracking gains in Chinese steel futures to rise 1.7 percent in London, and 2.1 percent in Shanghai. Zinc slipped as much as 1.8 percent in Shanghai after the ShFE on Friday reported a 23.3 percent jump in stocks before trimming losses to 0.5 percent. * NICKEL: The bulk of nickel moving out of London Metal Exchange-approved warehouses in Asia is showing up in hidden facilities in Europe, analysts said, denting a bullish scenario of potential shortages. * HKEX: A Shenzhen-based commodity exchange controlled by Hong Kong Exchanges and Clearing unexpectedly began spot trading on Friday, giving the HKEX much-coveted access to mainland China's market.