South African President Cyril Ramaphosa has authorised the deployment of additional soldiers to safeguard power stations in the country, citing sabotage and theft as a threat to supply of electricity.

The country has been witnessing unprecedented power shortages amid allegations of corruption at the state-run energy giant, Eskom.

Soldiers had in March been deployed to man power stations but their numbers have now been increased to 800 and their mandate extended to October.

Coded as Operation Prosper, the mission will see soldiers working with police officers "for the prevention and combating of crime and maintenance and preservation of law and order", the presidency said in a statement.

"Sabotage, theft and other crimes may threaten the functioning of power stations and the supply of electricity," it said.

Parliamentary speaker and the heads of provinces have been informed of the deployment, it added.

Known locally as load shedding, power blackouts have become a routine in South Africa, sometimes lasting for 15 hours a day, The crisis was declared a national disaster in February but the order was withdrawn in April.

On Thursday a high court ordered government to see that electricity supply to public hospitals, schools and police stations remains uninterrupted.