The problem affected the metropolitan area of São Paulo, the most populated area of the country as well as the states of Rio de Janeiro, Minas Gerais, Espírito Santo, Mato Grosso do Sul, Mato Grosso and Goiás, in southeastern and Midwestern Brazil.
According to information from CBN radio, Brazil's Mines and Energy Ministry was informed about the power cut and was trying to find how and why it happened.
Rio de Janeiro had heavy traffic jams at Linha Amarela and Avenida Brasil, among other arteries, due to the lack of working traffic lights. Resident were also unable to use electric appliance and TV sets, refrigerators and air conditionings stop working.
In the aftermath of the blackout energy companies didn't have any explanation for the power snafu. Several Internet sites, including some news sites went off the air.
Eletropaulo, the São Paulo power distributor with about 6 million customers, noted that the power failure "was a national problem that is being taken care of".
In Itaipu, one of the directors of the Itaipu complex said the trouble could have been the result of an error made by people inside the hydroelectric plant.
Brazil's Aneel, the National Agency of Electric power informed that it didn't know the cause of the problem and that it would announce its position as soon as it got official information.
In São Paulo, the Traffic Engineering Company (CET) told reporters that it had its hands full trying to organize the traffic in the city since traffic lights were not working. The Metro (subway) and the São Paulo Trains company stopped working, halted in their tracks.
According to Brazil's Minister of Mines and Energy, Edison Lobão, the most likely cause for the blackout was a heavy storm, which triggered the total shutting off of Itaipu.
The sudden reduction in energy then caused, in a domino effect, the shutdown of other lines connected to Brazil's National Integrated System for distribution of power.
Lobão informed that technicians had promised energy supply would go back to normal in a few hours, but he didn't expect to know the real cause of the blackout before Wednesday.
The president of Itaipu, Jorge Samek, said at the end of the day that he was 99% sure that a storm with heavy winds had been the cause for the blackout. Said he:
"In Foz do Iguaçu we had today heavy rains that knocked down trees of 40, 50 years, as if they were beach parasols." Itaipu, he explained, is responsible for 20% of Brazil's energy making it hard for other power plants to compensate when a shutdown like this occurs.