SAO PAULO, (Reuters – A major electricity outage  left tens of millions of people in Brazil’s two largest cities  of Sao Paulo and Rio De Janeiro without power last night.  

The Brazilian director of the Itaipu dam, the world’s  largest operational electricity generator which is on the  border between Brazil and Paraguay, told a radio station that  the power output of the entire dam was down.  

The website of local television Globo TV said other major  cities, including Belo Horizonte and the capital of Brasilia,  were also affected by the power cut. 
 
The electricity operator in the state of Minas Gerais said  the massive outage was caused by a problem at the Itaipu dam. 

The national electricity grid operator said 17,000  megawatts of energy had been lost, equivalent to the entire  consumption of Sao Paulo state.  

The subway system in Sao Paulo, Brazil’s financial capital,  was shut down by the outage, which occurred just after 10 p.m.  (0000 GMT) local time, leaving thousands of people stranded.  

Rio de Janeiro is due to host the World Cup soccer  championship in 2014 and the Olympic Games in 2016.