South Africa's state power utility Eskom urgently needs a turnaround plan as its capital structure is unsustainable, credit ratings agency Moody's said on Tuesday in a report which sent the rand to a two-month low.

A week ago Eskom reported a mammoth R20.7-billion ($1.39-billion) annual loss, and its outgoing chief executive said the firm needs to change its outdated business model to escape a "death spiral".

"The company's operational and financial performance has deteriorated, indicating the extent of the challenges facing Eskom in meeting its debt obligations absent government support," Moody's said in a note.

"The current capital structure is not sustainable... indicating a strong and urgent need for a longer term strategic turnaround plan."

The rand gave up its gains against the dollar and sharply reversed course after the report was published to hit its lowest since June 7. It traded down 0.4% at R14.9725 to the dollar by 15:19 GMT.

Struggling Eskom, which supplies more than 90% of the power in Africa's most industrialised economy but is dependent on government bailouts, is deep in crisis as its sales decline while debt-servicing costs soar.

It is regularly cited by ratings agencies as one of the main threats to South Africa's creditworthiness and economic growth.

Eskom's financial woes stem from a steep run-up in its salary, fuel and debt-servicing costs over the past decade, and it has also been hampered by mismanagement and corruption scandals under previous executives.

Last month the government proposed an extra R59-billion of support for Eskom over the next two years, in addition to R230-billion in bailouts spread over the next decade.

Moody's said the cash injections from the state were credit positive for Eskom but would do no more than stabilise the company's debt burden, and a long-term solution would still be needed.