JOHANNESBURG (Reuters) - South Africa's state-owned power utility will not be able to supply mines and other industrial customers with more than 90 percent of their electricity needs until 2012, Bloomberg reported on Wednesday.

Eskom, which supplies most of the nation's power, said last month it could not guarantee electricity to industry, prompting many large mines to shut for five days. The utility has since agreed to provide 90 percent supply to industrial customers.

In an interview with Bloomberg on Tuesday, Eskom Finance Director Bongani Nqwababa said the restrictions were unlikely to be lifted until the first new coal-fired power plants start up in 2012.

Eskom officials were not immediately available for comment.

Eskom plans to spend about 300 billion rand over five years to upgrade its infrastructure and improve power generating capacity in the country, which was hit by a wave of rolling blackouts last month.

South African President Thabo Mbeki and other senior ministers have apologised for the power crisis amid accusations that they ignored repeated warnings that the country would face electricity problems.

There are fears that the crisis could dramatically slow economic growth in South Africa.