MELBOURNE, March 23 (Reuters) - Base metals in Shanghai and London fell on Friday on fears that an escalating trade spat between China and the United States, the world's top two economies, could derail global growth and damage demand. In London, copper and aluminum hit the weakest since mid- December, while in Shanghai copper prices retreated towards levels not seen since mid-2017. Seasonally building inventories and deteriorating chart signals pointed to more downside near term.
* London Metal Exchange copper fell 0.7 percent to $6,650 a tonne by 0121 GMT having plumbed its weakest since mid December 2016. Prices extended a 1.4 percent fall from the previous session, breaking the 200-day moving average for the first time in around 18 months.
* Shanghai Futures Exchange copper tumbled 2 percent to 49,930 yuan ($7,885) a tonne, the weakest since July 2017.
* U.S. President Donald Trump signed a presidential memorandum on Thursday that could impose tariffs on up to $60 billion of imports from China, although the measures have a 30-day consultation period.
* China's commerce ministry said on Friday that the country was planning measures against up to $3 billion of U.S. imports to balance U.S. tariffs against Chinese steel and aluminum products, amid a brewing trade war between the two countries.
* A sell-off in steel spilled into inputs nickel and zinc. Shanghai rebar tumbled near 6 percent, while Shfe nickel slid near 4 percent. LME nickel fell 1 percent, adding to 2 percent losses from the session before.
* Shfe aluminum sank to its weakest since October 2016, hammered by concerns of rising China supply now pollution-linked output curbs have expired as well as U.S. trade tensions. LME aluminum held at its lowest since mid-December, having broken below the 200DMA mid-month.
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* Stock markets slid and perceived safe havens such as government bonds and the yen gained on Friday as investors rushed to safety after U.S. President Trump announced long-promised tariffs on Chinese goods, stoking fears of a global trade war.
BASE METALS PRICES 0135 GMT Three month LME copper 6640 Most active ShFE copper 49910 Three month LME aluminum 2063 Most active ShFE aluminum 13640 Three month LME zinc 3203 Most active ShFE zinc 24520 Three month LME lead 2338.5 Most active ShFE lead 18435 Three month LME nickel 13015 Most active ShFE nickel 98230 Three month LME tin 20750 Most active ShFE tin 142550
BASE METALS ARBITRAGE
LME/SHFE COPPER LMESHFCUc3 967.12 LME/SHFE ALUMINIUM LMESHFALc3 -1500.23 LME/SHFE ZINC LMESHFZNc3 458.56 LME/SHFE LEAD LMESHFPBc3 422.14 LME/SHFE NICKEL LMESHFNIc3 688.72
($1 = 6.3326 Chinese yuan renminbi)
(Reporting by Melanie Burton Editing by Kenneth Maxwell)