Massive blackout hits Brazil's major cities

A massive power outage has hit Brazil's two largest cities, Sao Paulo and Rio de Janeiro, leaving millions of people in the dark. The blackout occurred at 9 p.m. Tuesday, causing great disorder on the roads, as people were returning home from work.

The government has attributed the power outage to a shutdown in output at the Itaipu dam, which is located on the border of Brazil and Paraguay. But the exact cause remains unclear.

Tuesday's power failure is the most serious one in Brazil since 2001. Electricity has been restored in some areas of Sao Paulo and Rio de Janeiro, but officials say a complete recovery will take time.