Officials in Brazil say a bolt of lightning was responsible for plunging more than sixty million people into darkness in the country's worst power cut in fifteen years.

The lightning struck an electricity substation on Thursday night, causing a chain reaction that knocked out the power grid across south and southeastern Brazil for several hours.

The blackout paralysed the two main cities, Sao Paulo and Rio de Janeiro.

Hundreds of people were stuck on the roads after traffic lights went off; others were trapped on the underground system.