SYDNEY, Dec 9 (Reuters) - The likelihood of more power outages...

SYDNEY, Dec 9 (Reuters) - The likelihood of more power outages in key Australian mining and manufacturing state South Australia is high as the Southern Hemisphere summer approaches, a business group said on Friday.

A blackout in September caused by lightning storms brought some of the world's biggest mining and metals-refining businesses to a standstill, leading to criticism of local power suppliers by mining giant BHP Billiton (BHP) .

The outage cost businesses a total A$367 million ($273 million, according to a survey by Business South Australia.

BHP's Olympic Dam copper mine was left without power for two weeks, costing the world's biggest miner an average 567 tonnes in lost output a day, worth about $3 million daily.

The survey by Business South Australia found almost a third of the cost when storms swept across the state on Sept. 28 knocking out the electricity network was borne by BHP and fellow copper miner Oz Minerals (OZL), lead refiner Nyrstar NYR.BR and Arrium Steel (ARI).

"Business SA and the broader business community have serious concerns that this summer, if there are consecutive days of extreme temperatures, that is going to place additional pressure on the interconnectors and we're going to have rolling brown outs," the group's executive director, Anthony Penney told reporters.

The state should expect higher-than-average temperatures between December and February - the Southern Hemisphere summer months - as extreme weather engulfs much of the eastern half of Australia, according to the Bureau of Meteorology.

State energy supplier Electranet said it was looking at options for building high-voltage electricity interconnectors it could link with other states.

($1 = 1.3421 Australian dollars)