Johannesburg - Eskom could seek to borrow up to $1bn a year from the World Bank over five years after a ratings downgrade made it more difficult to borrow on financial markets, the Business Day newspaper reported.

The newspaper said on Wednesday the power utility would turn to the World Bank due to tough global markets and after a Moody's downgrade, which will likely raise the cost of borrowing money it needs for a major upgrade.

It quoted Eskom finance director Bongani Nqwababa as saying the state-owned company was "rechecking" its funding strategy and was likely to focus on borrowing locally from development agencies such as the World Bank and African Development Bank and from export credit agencies.

Eskom officials could not immediately be reached for comment. A World Bank spokesperson said the bank was in an "ongoing dialogue" with Eskom but declined further comment.

Business Day did not provide a source for the $1bn a year figure.

Eskom is to spend billions of dollars to boost power capacity as demand outstrips supply in Africa's biggest economy.

A wave of blackouts has cost South Africa billions of rand in lost productivity and unnerved foreign investors.

Ratings agency Moody's said on Monday it had cut Eskom's local currency rating to Baa2 from A1 and cut the foreign currency rating to Baa2 from A2. The outlook for all ratings was negative.

The agency blamed the four notch local currency downgrade on a deterioration of Eskom's stand-alone credit profile due to an aggressive capital investment programme and the fact Eskom was not able to raise tariffs as much as it had requested.

The National Treasury has budgeted R60bn over the next three years to help Eskom pay for its R343bn, 5-year expansion programme.