Rio Tinto Alcan's Lynemouth aluminium smelter in Northumberland is still running at a reduced rate following a power cut in December which knocked out more than half its capacity, a spokesman said on Thursday.

One production line (potline) is completely down and 25 percent of the other is also down. No decisions have been taken yet on pot restarts John McCabe, corporate affairs director, Alcan Aluminium UK Limited said in an e-mailed response to questions.

Some industry watchers question whether the company will restart the pots, especially since in November, Rio Tinto, one of the world's top producers of aluminium, said it was set to close the Lynemouth smelter as rising energy costs put pressure on margins.

A consultation process on its closure is in progress and due to continue to the end of February.

Production problems are not confined to just Lynemouth.

On Wednesday, Rio Tinto declared force majeure on aluminium output from its Alma and Shawinigan smelters in Quebec.

The firm started slashing output at the 438,000 tonnes per year (tpy) Alma smelter on January 1, when it locked out more than 750 unionised workers after contract talks broke down.

It has also been forced to curb production by 50 percent at its 100,000 tpy Shawinigan plant following a circuitry failure.

A spokesman said it had yet to decide whether it would bring the idled capacity at the smelter back on stream before operations are due to wind down permanently by December 2014.

McCabe said the power cut at the 175,000 tpy Lynemouth smelter had been caused by an instrumentation failure with a grid transformer.

(Reporting by Karen Norton)