The outage also briefly plunged the whole of neighbouring Paraguay into darkness

Candles and car headlights were the only illumination in Brazil's two biggest cities as a huge power cut brought chaos.

Tens of millions of people in Rio de Janeiro and Sao Paolo and cities in at least four other states were plunged into darkness.

Traffic ground to a near standstill.

Trapped subway passengers had to make their way along the tracks to the next station to escape.

Rio's international airport has its own emergency generators.

Flights were still coming and going but travellers were delayed as cabbies refused to drive through crime-ridden areas in the dark.

For residents the street was a more comfortable place to spend the evening than sweltering at home.

[Ricardo de Sousa, Resident of Rio de Janeiro]:
"It's too hot at home. I can't stay inside. It's so hot that I have to stay out here on the street riding my bike until it gets better."

The power began to come back on after three hours.

The outage also briefly plunged the whole of neighbouring Paraguay into darkness,

It's being blamed on transmission problems from a huge dam that supplies hydro-electric power to both nations.