Tanzania, May 20 -- Johannesburg. South Africa's state-owned power utility Eskom has warned it may throttle electricity supply to Johannesburg after the country's largest city and key economic hub failed to settle billions of rand in overdue payments.

In a statement issued on Tuesday, Eskom said the City of Johannesburg and its electricity distributor, City Power, owed arrears amounting to 5.26 billion rand (about $315 million), with an additional 1.58 billion rand due by June 5.

Eskom said it had issued a formal notice signalling its intention to "reduce, interrupt and/or terminate the supply of electricity" to selected bulk supply points serving the municipality and City Power.

The utility said it had engaged the Johannesburg metropo...