RIO DE JANEIRO — Brazil emerged early Wednesday from a widespread power outage that plunged as many as 60 million people in at least nine states into darkness for hours, prompting security fears and concern from residents about another black eye for a country hosting the 2016 Olympic Games.

Power went out for more than two hours in Rio de Janeiro, Sao Paulo and several other major cities after transmission problems knocked one of the world's biggest hydroelectric dams offline. Airport operations were hindered and subways ground to a halt.

All of neighboring Paraguay also went dark, but for less than a half hour. A spokesman at Brazil's Energy Ministry said up to 60 million people — nearly a third of the nation's population — were affected by the blackout. He spoke on condition of anonymity, as he was not authorized to discuss the matter.

Brazilian authorities blamed storms that took down power lines and towers, causing a domino effect that rippled across the region.

Lights twinkled back on along Rio's Copacabana beach, in South America's largest city of Sao Paulo and in Paraguay's sleepy capital of Asuncion. But some traffic lights were still out in both Rio and Sao Paulo and traffic officials were expecting drivers to face difficulties the rest of the day, according to local media.

In Rio, Governor Sergio Cabral sent an elite police unit into the streets early Wednesday to help maintain calm in a city known for its crime. The mayor dispatched 300 extra unarmed civil guards to help control traffic.

The city saw a spike in robberies around the Maracana football stadium — where the opening and closing ceremonies of the 2016 Olympics will be held, along with the 2014 World Cup final. A police spokesman said a band of roughly a dozen criminals worked the area together, robbing people en masse — a crime phenomenon so routine it is known as a "big sweep."

The spokesman, who talked on condition of anonymity as he was not authorized to discuss the matter, didn't say how many robberies occurred or how many happen in an average night in the area, but said there were more than usual during the blackout. He said elsewhere in Rio there did not appear to be much of an increase in crimes, which he in part attributed to commuters staying within the safety of train and subway stations until energy was restored.

Questions remained about what happened and what the fallout would be in Brazil, a nation seen as an ascending economic and political power.

"The image of Brazil, of Rio, is bad enough with all the violence," said 35-year-old graphic designer Paulo Viera, as he sat in a restaurant a block from the sandy arc of Copacabana.