Efforts are continuing to rescue the remaining 700 workers trapped deep underground in a South African gold mine .

So far more than 2,500 have been safely brought to the surface of the Elandsrand mine at Carletonville, southwest of Johannesburg.

The first miners emerged over 15 hours after being trapped. The operation is expected to continue for some time.

The workers, including 150-200 women, became trapped around 2,200m below ground yesterday morning after a power cut caused a lift malfunction.

South Africa mapThe mine owners say investigations will be carried out into what happened, but are confident that all personnel will be safely brought up.

The National Union of Mineworkers (NUM) said it suspected negligence was behind the accident and vowed to push gold firms to build emergency exits in the mine.

The union said there is no time to make adequate checks because of continuous operations.

An NUM spokesman said the miners were trapped in a cramped space where temperatures could reach 30 to 40C.

The miners were caught after an air pipe broke off and hurtled down the shaft, damaging steelwork and severing an electrical cable carrying power to the main lift.

Rescuers were in contact with the trapped miners and clean air and water were being pumped down to them. A smaller lift close to the main elevator is being used in the rescue operation.

South African gold mines are the deepest in the world and unions have often criticised companies for not doing enough to ensure workers' safety.

Gold mine operations have come under scrutiny over the past few months following a series of accidents, as gold producers mine ever deeper to offset lower production and reap the benefits of a sharply higher bullion price.

Gold output in South Africa, the world's biggest gold producer, has tumbled by over 50% over the past decade, as high-grade mines run out of ore and firms grapple with more difficult and high-cost underground operations.