South Africa is weighing extra options to support Eskom, including swapping the financially troubled State power firm's debt for government bonds or ring-fencing it in a special account, a senior treasury official said.

Discussions are at an early stage, and it is not yet clear which option will be chosen to help Eskom, which has this year been forced into implementing rolling power cuts across the country that have hurt local businesses.

President Cyril Ramaphosa has already pledged R230-billion of financial support over the next ten years, but officials say other steps will be needed to make the firm financially sustainable.

Ian Stuart, acting deputy director general for National Treasury's budget office, said various scenarios were being considered for resolving the "large and complex" issue, with implications for South Africa's credit rating a key criterion.

"We are looking at which option is best both in terms of fiscal costs and support for the reform process," he told Reuters.

Support could take the form of ongoing subsidies, or the firm's debt could be moved off its balance sheet to the government or into a special purpose vehicle.

"A switch to South African government bonds will be looked at, but we have to confirm the legalities of each option and implications for ratings agencies," Stuart said.

Of the major credit agencies, only Moody's still rates South Africa at investment grade, on the lowest such rung on its scale.

Ramaphosa's government has sought to reassure the agencies that it has a credible plan to rescue Eskom without putting public finances at risk.

Moody's did not immediately respond to a request for comment.

Eskom said in a statement that it had held "extensive consultations with key government departments regarding the proposed support structures that are currently being considered for the company".

The power utility had around R440-billion of debt as of March, of which more than R270-billion was government-guaranteed. In 2018, South Africa's gross domestic product was $366-billion, according to World Bank data.

Eskom is due to release results this month that could show a loss of as much as R20-billion for the financial year to the end of March.

The government is also expected to soon announce the appointment of a chief restructuring officer at Eskom who will have an important say in deciding which of the additional support measures are chosen.