Labourers pull electricity cables to be laid underground. File picture: Amit Dave/Reuters

Johannesburg - Johannesburg's City Power said on Tuesday that it had restored at least 27 percent of the power in the inner city following a fire at an underground tunnel that was caused by cable thieves. 

City Power said the damage to the cables had resulted from fire during the attempted cable theft on Sunday morning, affecting multiple feeders and load centre at various sub stations in the central business district.

As a results, multiple areas in Johannesburg have experienced power outage in the inner city.

Affected areas include Carlton Centre, the Premier's Office, and multiple buildings and streets on Jeppe, Plein, Pritchard, President, Albert Sisulu, Bree, Marshaltown, Karzene, Selby and Durban streets.

On Monday, City Power operators gave a 24-hour estimate to complete the repairs before they can back feed as they discovered that there were still cables burning which needed to be put off. Operators have to run tests on the cables to check if they were affected by the fire before replacing them.

City Power spokesperson, Sol Masolo, said the operators were working around the clock to restore power in the inner city.

Masolo said electricity supplies had been restored to Marshalltown on Monday night. The restoration represented 27 percent of the power restored so far.

"Johannesburg has a network of about 20 kilometres of underground tunnels. So it is very difficult for me to say where the affected tunnel is located because you would even be allowed there," Masolo said.

There were also concerns that the underground fires could have left dangerous fumes.

"Early this morning the environmental and safety experts determined that it is safe for our technicians to enter the underground tunnels. This paves the way for our technicians to enter the tunnels and begin with the technical assessment on the extent of the damage to the underground cables."

Masolo said the resumption of the repair process will proceed after the technical assessment has been completed. He said the assessment will also determine if any cables were stolen.

"City Power once more apologises to all affected customers and will do everything in its power to ensure that electricity is restored as speedily as it is humanly possible."