Blackouts in South Africa may worsen as rain dousing coal stockpiles at power plants renders the fuel unusable, Eskom said yesterday.

The outages, which began on Tuesday, may extend beyond tomorrow (subs: Friday) and affect aluminium smelters owned by BHP Billiton in South Africa and neighbouring Mozambique, Eskom spokesman Fani Zulu said yesterday. About a fifth of Eskom's generating capacity is offline and rain may cut output from another two power plants.

"There is lower supply and higher demand'' because of the weather, Zulu said. The only method "you have to force that down is through load shedding".

Outages hit BHP's smelters, ArcelorMittal's steel plants, and coal and gold mines owned by Anglo American Plc.

All three of BHP's smelters in Richards Bay and Maputo were affected yesterday, adding to disruptions yesterday, Bronwyn Wilkinson, a spokeswoman for the company said.

"We are affected but in a controlled manner," Tami Didiza, a spokesman for Mittal Steel South Africa, said yesterday. He didn't say which plants were affected by power rationing, or to what extent.