The South African government says the theft degraded state-owned power plants and contributed to an electricity crisis that has hit the country.

The gang diverted trucks carrying high-grade coal to power stations, stealing the coal to sell, and replacing it with sub-standard fuel, the country’s tax and revenue agency said in a statement. 

The South African Revenue Service carried out the operations in the Gauteng, Mpumalanga, KwaZulu-Natal, Free State and Limpopo provinces. 

No arrests have been made yet, national police spokesperson Brigadier Athlenda Mathe said.

Africa’s most advanced economy is in the midst of a power crisis that has resulted in scheduled rolling blackouts because its coal-fired stations are not generating enough electricity for the country’s 62 million people.

The state-owned power utility, Eskom, produces about 95 per cent of South Africa’s electricity.

The blackouts have been largely blamed on years of corruption and mismanagement at Eskom, though authorities also have said that suspected organised crime syndicates have been operating for years around Eskom's power station supply chains.

Suspects involved in the syndicate include former Eskom employees, the tax agency said.

The switching of coal destined for state-owned plants has worsened the country’s electricity crisis, the agency said.

“The low-grade coal damages the infrastructure at the Eskom power stations, which is a major factor in crippling the power utility’s ability to generate electricity for the South African grid,” it said.

South Africa experienced its worst blackouts ever at the start of the year, when homes and businesses went without electricity for more than eight hours a day. 

South Africa has national elections next year, when the power crisis is likely to be a key issue for voters.