SINGAPORE/BEIJING, Jan 17 (Reuters) - London copper prices rose for a third straight session on Thursday as China's move to inject liquidity into the financial system boosted expectations of higher demand in the world's top industrial metals consumer. The People's Bank of China is injecting 250 billion yuan ($37 billion) through seven-day reverse bond repurchase agreements and 150 billion yuan through 28-day reverse repos, traders said. Shanghai copper has flipped into backwardation amid a promise of value-added tax (VAT) cuts in China, which has increased near-term demand for physical copper in the world's top consumer of the metal, Jinrui Futures said in a note. The tax reductions are not expected to be formalised until March but Jinrui Futures said their implementation could result in a 400 yuan a tonne boost to the ShFE copper price for every percentage point VAT decrease. Refinitiv Eikon data shows a 10 yuan a tonne contango between the March and April ShFE copper contracts but a 130 yuan a tonne backwardation from April to May. FUNDAMENTALS * COPPER: Three-month copper on the London Metal Exchange was up 0.1 percent at $5,987 a tonne by 0512 GMT, while the most-traded March contract on the Shanghai Futures Exchange ended the morning up 0.5 percent at 47,410 yuan ($7,006.68) a tonne. * ZINC: The metal used to galvanise steel rose as much as 1.8 percent to 20,960 yuan a tonne, its highest since Dec. 12. "Spec positioning is largely flat now on our estimates on both LME and ShFE" zinc, Marex Spectron said in a note. * ALUMINIUM: Aluminium led the rest of the LME complex lower, falling 0.7 percent to $1,846.50 a tonne after the U.S. Senate on Wednesday rejected legislation to keep sanctions on companies linked to Russian oligarch Oleg Deripaska, including aluminium firm Rusal. * ALCOA: Top U.S. aluminum producer Alcoa Corp beat Wall Street estimates for quarterly profit on Wednesday, buoyed by strength in its alumina segment, but shares slipped after the company did not provide a closely watched profit measure for the full year.