A massive blackout spanning 11 states in northeastern Brazil plunged nearly 53 million residents into the dark early on Friday morning. The event, caused by a "total collapse" of the northeastern grid, has raised concerns about electric reliability in South America’s largest economy, which is gearing up to host the World Cup soccer tournament in 2014 and the 2016 Olympic Games.

Brazil’s transmission grid is segmented into independent regional power grids that form an interconnected national network consisting of more than 40,000 miles of transmission lines. The event began 14 minutes after midnight on Friday, caused by a "short circuit" on the 500-kV Hills-Empress transmission line, part of a link between the South/Southeast/Midwest and North/Northeast grid systems, said national grid operator Operador Nacional do Sistema Elétrico (ONS) in a press release on Friday.

The event separated the North/Northeast grid from the rest of the national interconnected system (or "SIN"), and with the isolation of the northeastern grid came a sharp drop of voltage and frequency that caused the total shutdown of loads in that region totaling 9,500 MW, ONS said. In the North, meanwhile, 3,400 MW—or 77% of total load—was shut down. The Southeast, South, and Midwest grids were not affected.

The systems were restored about four hours after the failure occurred.

The federal Ministry of Mines and Energy on Wednesday said in a press release that the Oct. 26 disturbance stemmed from a "combination of human error with procedural error," citing a new ONS report. ANEEL, the federal energy regulatory authority was "studying sanctions" to be applied to TAESA, a Cemig-subsidiary, that is responsible for the failed transmission line in the north and northeastern regions.

"The origin is being investigated so that we can identify precisely what occurred," Acting Minister of Mines and Energy Marcio Zimmermann told reporters on Wednesday.

"We cannot afford mistakes like this in the Brazilian system," ANEEL director Nelson Hubner said at the press conference. "Let’s change the rules to correct these failures."

The Brazil blackout comes just months after the failure of India’s Northern, Eastern, and Northeastern grids, which cut power to more than 670 million people in an area that stretched 2,000 miles. But it is not Brazil’s biggest power failure. The country with a population of 196 million saw an even larger blackout on the night of Nov. 10, 2009, when 60 million people in 18 of the country’s 26 states—including its largest cities, Sao Paulo and Rio de Janeiro—were plunged into darkness after three transmission lines that deliver power from the 14-GW Itaipú dam failed and took 28.8 GW out of the system.

That blackout brought flashbacks of an energy crisis that had almost crippled the nation’s development in 2001. Despite reforms, experts warned after the 2009 debacle that the country, stricken by an inability to expand its electricity supply as planned, was still poised to see a serious generating gap due to its booming population and robust economy—a scenario likened to that before the 2001 crisis. Foremost among concerns about the nation’s reliability is a marked reliance on hydropower coupled with a vulnerability to drought.

In February 2011, seven northeastern states saw a brief blackout, originating in a substation. The country’s most dramatic blackout occurred in in 1999 after lightning struck a power substation in Sao Paulo state and left 97 million Brazilians without power for up to five hours.