State-owned electricity company Eskom said on Wednesday its power stations continued to operate optimally in line with contingency measures put in place to mitigate the impact of a wage strike.

Workers are protesting the company's decision not to hike wages this year. They have demanded a 15 percent increase across the board. 

"Eskom’s power stations and other critical facilities continue to operate optimally in line with the contingency measures that the company has put in place to ensure security of power supply during this period of wildcat strikes," the utility said.

"There are, however, a few isolated incidents where some protesting workers tried to blockade the entrances of our power stations, but these situations have been quelled by the presence of the public order police," it added, saying the situation was tense but stable.

Eskom says it cannot raise wages due to its difficult financial situation.

But unions representing its workers, namely the National Union of Metalworkers of South Africa and the National Union of Mineworkers, say the company, whose former senior executives were pushed out over corruption charges, is dealing with "a self-imposed crisis".