A turbo-generator exploded and caught fire at Duvha power station near Witbank in Mpumalanga on Wednesday morning, Eskom said.

No one was injured in the accident which happened shortly after 6am, Eskom spokesman Tony Stott said.

"If it had happened at 8am, people would likely have been injured and could even have been killed," said Bennie Blignaut, of the trade union Solidarity.

"This was one of the largest explosions in the industry."

But Stott said he did not think the time would have made a difference.

"It is not as if people were not working there at the time."

Stott said unit 2 of the power station was in the process of being returned to service after an outage when the turbo-generator malfunctioned.

"It damaged itself explosively and caught fire."

The station's fire-fighting and emergency teams, along with Witbank's fire department and emergency services, brought the fire under control.

There were no interruptions in power supply, and the other units continued to operate, Stott said.

"The unit is stable in shutdown conditions pending a technical investigation of the incident."

Blignaut estimated the damage at about R2-billion, but Stott said he the extent would only be established through an investigation.

According to Blignaut, the units were over 20 years old.

"Poor maintenance could have been the cause," he said.

Eskom was using fewer people, and employing contractors, rather than permanent staff, Blignaut said. "For us it is all about safety."

He called for a commission of inquiry into the incident, of which Solidarity wanted to be part.

Stott said it was premature to speculate about the cause of the accident before the technical investigation had taken place.

He said the age of the generators was not a cause of concern for Eskom.

Stations like Duvha were designed to last at least 40 or 50 years. Their maintenance schedules were also designed to ensure they were kept running, Stott said.

Eskom's head office would put an investigating team together. It had to report to the inspector of machinery at the Department of Labour.

If necessary, technical experts would also be brought in, he said