* LME metals extend mammoth overnight gains ahead of US data
* Shanghai copper and zinc limit up after LME rally
* Tin bounces almost 50 pct in less than a week
* Markets may have bottomed, risk starting to favour longs

London copper futures rose almost 2 percent on Thursday, extending Wednesday's 12.6 percent surge, while Shanghai copper and zinc surged by their 4 percent upside limit, chasing the sharp rally in international prices.

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