South Africa's troubled state-run electricity firm, Eskom, says 11 of its power plants have been shut down.

The country is in it fourth day of severe power cuts, which have caused transport problems in the main city Johannesburg, with many traffic lights switched off.

A joint press briefing by Eskom chairman Jabu Mabuza and Minister of Public Enterprises Pravin Gordhan is being broadcast live by state broadcaster SABC.

Eskom has said it's working around the clock to return more generating capacity to the network and has appealed to customers to turn off all non-essential lights and appliances.

The power cuts South Africa's ageing network has suffered from years of under-investment and mismanagement, correspondents say.

Last month, the government announced a $5bn (£3.7bn) bailout of Eskom, as well as plans to break up the company.