Mining group BHP Billiton said on Friday it had been hit by power cuts earlier this week at its smelters, but added that interruptions to supply were short and did not affect output.

Aluminium smelters are among the biggest industrial consumers of electricity.

BHP spokesman Maredi Mogodi told Reuters the cuts lasted just under an hour, and a loss of power for about two hours or more would have led to production declines.

He said the cuts were as a result of South African state utility Eskom [ESCJ.J] being unable to supply electricity.

BHP, the world's sixth-biggest producer of primary aluminium, runs three smelters in southern Africa, which produce close to 1.5 million tonnes a year of aluminium.

Mogodi said the cuts were over and above the 10 percent power reduction that Eskom had ordered big consumers of power to shed, in order to cut electricity demand.

Fortunately there was no loss in production. But it is a bit of a nuisance that leaves us hanging by the skin of our teeth, Mogodi said. We would only feel the impact of loss in output if the supply was cut for two hours or longer.

Mogodi said BHP was able to store power at the smelters and use it to keep its pot lines at the required temperature so that it did not suffer a loss of output.

Eskom had warned that a risk of load-shedding had increased significantly on Thursday as technical problems put strain on its electricity grid, but said it had not interrupted power supplies. On Friday it said that this risk had decreased.

BHP said in March it would halve operations at its Bayside aluminium smelter in South Africa to curb power demand and help the country recover from an electricity crisis. Its other smelter in South Africa, Hillside and Mozal in Mozambique would operate on 90 percent of their power needs.

Total annual production loss would be just over 120,000 tonnes across all three smelters. (Reporting by James Macharia, Editing by Peter Blackburn)

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