Power has been largely restored to much of southern Brazil after a four-hour blackout that plunged the country's biggest cities into darkness, triggering a crime alert.
Brazil's Energy Minister Edison Lobao says the outage, which affected tens of millions of people, originated at the country's biggest hydroelectric plant, Itaipu, on the border with Paraguay, but the exact cause is not yet known.
The country's largest cities, including Sao Paulo and Rio de Janeiro among others, were left with no illumination or traffic lights and public transport was halted due to the outage.
Belo Horizonte and the capital Brasilia were also affected.
It also prompted a major police mobilisation amid fears of an opportunistic crime wave.
In Paraguay, a power cut blacked out the whole country for up to 15 minutes but electricity has been restored.
The southern states of Sao Paulo, Rio de Janeiro, Minas Gerais, Espirito Santo, Mato Grosso do Sul and parts of the central state of Goias and the federal district of Brasilia all lost power at 10pm local time.
The national electricity grid operator says 17,000 megawatts of energy were lost, equivalent to the entire consumption of Sao Paulo State.
The Itaipu power plant provides about 20% of the electricity supply in Brazil, Latin America's largest economy, and more than 90% of Paraguay's.