Panic, fear and confusion have gripped Brazil after a power cut plunged millions of people into darkness. Rio de Janeiro and São Paulo were without light for several hours when the blackout happened just after 10pm.

It affected 12 states, lasted for four hours, and stretched as far as neighbouring Paraguay, raising questions about Brazil’s ability to host two global sporting events in a few years’ time.

In São Paulo’s dangerous city centre, frightened groups of people clustered together for protection and ran through the streets, terrified that criminals would take advantage of the darkness and confusion. São Paulo’s main police emergency number was left powered by one generator and the Polícia Civil lost all contact. The streets of Rio were patrolled by paramilitary troops.

Maria Das Dores Alves Dias was in class at the Caetano de Campus college in central São Paulo when the lights went out on Tuesday. “Everyone was shouting. I was scared. We all followed the emergency lights to get outside,” she said.

Underground trains ground to a halt in Rio and São Paulo, leaving passengers stranded in the tunnels. Fixed telephone lines failed and mobile phone networks were jammed. Thirty-two people were trapped in lifts in São Paulo.

Children in intensive care at the Santa Isabel maternity hospital in Bauru, São Paulo, had to be moved because the public hospital does not have a back-up generator. “Suddenly everything went black,” Fábio Tadeu Texeira, the administrator, said. “We moved all the children to a nearby hospital. We didn’t know when the power would come back and I was anxious for the light to return.”

The Governor of Rio, Sérgio Cabral, sent a police unit into the streets to help to maintain calm. Around the Maracanã stadium, where the opening and closing ceremonies of the 2016 Olympics will be held, as well as the 2014 World Cup final, a band of criminals robbed people — a crime phenomenon so routine that it is known as a “big sweep.”

A spokesman for the Ministry of Mines and Energy said that three transmission lines carrying electricity from the giant Itaipu dam, which provides 20 per cent of Brazil’s electricity, failed in three cities.

“We have technicians working out what happened and analysing the causes. The most likely cause is strong rain, though this is not yet official,” he said.

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