METALS-Aluminium slips ahead of Chinese smelter restarts

* LME/ShFE arb: http://bit.ly/2wZSAEz (Updates throughout, moves dateline from BEIJING)

LONDON, March 12 (Reuters) - Aluminium prices fell on Monday, three days before the end of winter output curbs in top producer China, as investors worried that supplies are too plentiful to keep prices near six-year highs.

Benchmark aluminium on the London Metal Exchange (LME) was down 0.3 percent at $2,113.50 a tonne at 1159 GMT. Prices have slipped around 8 percent from a high in early January.

Aluminium on the Shanghai Futures Exchange (SHFE) closed at the lowest in 14 months.

Prices have been pressured by sharp increases in stocks of aluminium in SHFE and LME warehouses, despite restrictions on Chinese smelter production from Nov. 15 to March 15. <AL-STX-SGH> <MALSTX-TOTAL>

Industry sources say there may only be a limited restart by these smelters from March 15 because prices are not high enough for some to break even.

Any increase in output could drive prices lower.

"We are going to trend down below $2,100 in the fist half of the year because of this China surplus," ING analyst Oliver Nugent said.

But he said prices on the LME would likely rise again later in the year because of a persistent shortage of metal outside China.

ALUMINIUM SPREADS: The price of cash aluminium has fallen below the three-month price, suggesting greater nearby availability of metal and taking pressure off prices. <MAL0-3>

PREMIUMS: Some Japanese aluminium buyers have agreed to pay some global producers a premium of $129 per tonne for shipments in the April to June quarter, the highest in three years.

COPPER: LME copper was down 0.9 percent at $6,900 a tonne after a rise in inventories in LME-registered warehouses of 10,000 tonnes to 321,125 tonnes suggested ample supply of the metal. Prices remain near 4-year highs hit in December. <MCUSTX-TOTAL>

STRIKE: Workers in the largest union at Antofagasta's Los Pelambres copper mine in Chile rejected an offer for a new labour contract, paving the way for a strike. Los Pelambres produced around 350,000 tonnes of copper last year.

The potential strike has revived concerns that labour disputes will disrupt production this year, supporting prices.

POSITIONING: Speculators reduced bets on higher prices, with the net long in Comex copper falling to the lowest since November 2016.

OTHER METALS: LME nickel was down 0.7 percent at $13,765 a tonne, zinc was 0.6 percent lower at $3,257, lead slipped 1.2 percent to $2,348.50 and tin was flat at $21,400.

(Additional reporting by Tom Daly, editing by Ed Osmond)