* Aluminium touches lowest in six weeks
* GRAPHIC-2018 asset returns: http://tmsnrt.rs/2jvdmXl
* LME/ShFE arb: http://bit.ly/2wZSAEz (Adds more analyst comment, updates prices, changes dateline from MELBOURNE)
LONDON, Feb 8 (Reuters) - Copper extended its downtrend on Thursday, touching its lowest in nearly eight weeks, after another big rise of inventories highlighted the market currently has healthy supplies.
On-warrant copper inventories in warehouses certified by the London Metal Exchange MCUSTX-TOTAL> - those not earmarked for delivery - jumped by 25,700 tonnes on Thursday and have surged by 75 percent over the past three weeks.
That showed that a 12 percent rally in LME prices in December was not supported by the underlying fundamentals, some analysts said.
"This correction has been needed to put metals prices in line with the fundamentals, which are not bearish but also not that bullish," said Gianclaudio Torlizzi, Partner at consultancy T-Commodity in Milan.
"Copper has broken its $6,860 support level, so there's still space for more of a correction lower. I don't think we'll go much lower than $6,500, which would be a good buying area."
* COPPER: LME copper was down 0.8 percent at $6,826 a tonne by 1100 GMT after hitting $6,809, the weakest since Dec. 15 and extending sharp losses from the previous session when prices fell 2.8 percent.
* TECHNICALS: Prices also pierced support at the 100-day moving average near $6,883, damaging copper's technical picture.
* TRADE DATA: Helping to cushion the falls was data showing that China's trade machine kicked up a gear in January after stumbling the previous month, with exports and imports both growing much more than expected.
* IMPORTS: China's unwrought copper imports fell for a second straight month in January as winter restrictions on the construction sector and high domestic production rates continued to crimp demand for metal from overseas.
* SCRAP CONCERNS: Traders were likely to import more copper cathode to China given uncertainty over smelter feed supply as new restrictions on China's scrap imports come into force, said analyst Dan Morgan at UBS in Sydney. "I think imports will be strong in the first half of the year."
*ZINC SHORTAGES: LME zinc bucked the weaker trend and edged up 0.1 percent to $3,383 a tonne, supported by continued tight supplies.
Zinc smelters are set to accept lower fees for processing concentrate into metal when annual contracts are hammered out next week at a conference in California, as a crunch in mine supply stretches into a third year.
* ALUMINIUM: LME aluminium dropped to $2,148, the lowest since Dec. 22, before paring losses and trading unchanged at $2,158 a tonne.
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(Additional reporting by Melanie Burton in Melbourne, editing by David Evans)