ArcelorMittal South Africa, a unit of the world's top steelmaker, said recently that the failure of the furnace at its Newcastle plant would result in a loss of 400,000 tonnes in output and the financial impact would be "substantial".

It also said in a statement that the blast furnace would take about three months to repair.

"ArcelorMittal South Africa management is in the process of exploring options to augment the supply to meet the domestic customer requirements for the next three months," it said.

"The financial impact is estimated to be substantial considering the potential sales volume loss. Insurers were notified of the incident and a claim will be submitted once the actual repair costs and consequential losses are finalised," it added.

The company had said on Wednesday that the furnace at its gas cleaning plant had failed and the dust catcher had partially collapsed.

The company's outlook is already subdued.

Higher input costs and a strong rand led to a 63 percent drop in the company's first-half profit and the steelmaker forecast a difficult third-quarter, partially due to a recent strike over wages and a planned maintenance shutdown at one of its plants.