South Africa has chosen five countries to compete for its nuclear power programme, the government said Wednesday, as it looks to the controversial energy source to boost flagging output.

Russia, France, China, the United States and South Korea have signed preliminary agreements in "the "preparatory stage for the procurement process," the president's office said in a statement.

Africa's second largest economy is battling to meet the rising demand for electricity, with regular blackouts blamed for limiting economic growth and productivity.

South Africa has one nuclear power station but relies heavily on coal for electricity generation by the state-owned power firm Eskom.

The government envisages building 8 nuclear reactors worth up to $50 billion (40 billion euros) to add 9,600 megawatts of generating capacity, or nearly one-third to the current estimated capacity of 33,000 megawatts.

The move has met resistance from environmental groups who have questioned the cost and safety of the project.

The government said it had held workshops with vendor countries to allow them to demonstrate their capabilities, marking a "significant milestone" in the pre-procurement phase.