Hallways of Buenos Aires's subway are lit only by emergency lights during a blackout, in Buenos Aires, Argentina, Sunday, June 16, 2019. (Photo: AP) 

The lights were back on Monday across Argentina, Uruguay and Paraguay after a huge blackout that affected tens of millions people, but authorities remained in the dark about the cause of the grid collapse and continued to calculate the economic damage.

Argentine President Mauricio Macri promised a thorough investigation into what he called an “unprecedented” outage, one that raised questions about flaws in South America’s power grid, which connects many of the region’s largest countries.

Energy officials said the results of the investigation would be available in 10 to 15 days, and they could not immediately provide details on the economic impact of the outage, which happened on a Sunday, a day before a national holiday in Argentina.

“From zero to 10, there is zero chance that this will repeat itself. It can’t repeat itself,” Argentine Energy Secretary Gustavo Lopetegui said Monday.

The blackout originated at an electricity transmission point between the power stations at Argentina’s Yacyretá dam and Salto Grande in the country’s northeast “when the system was getting too much power” Lopetegui said. Although these types of failures have happened in other countries as well, he said a chain of events took place that caused a total disruption.

The lights were back on Monday across Argentina, Uruguay and Paraguay after a huge blackout that affected tens of millions people, but authorities remained in the dark about the cause of the grid collapse and continued to calculate the economic damage.

Argentine President Mauricio Macri promised a thorough investigation into what he called an “unprecedented” outage, one that raised questions about flaws in South America’s power grid, which connects many of the region’s largest countries.

Energy officials said the results of the investigation would be available in 10 to 15 days, and they could not immediately provide details on the economic impact of the outage, which happened on a Sunday, a day before a national holiday in Argentina.

“From zero to 10, there is zero chance that this will repeat itself. It can’t repeat itself,” Argentine Energy Secretary Gustavo Lopetegui said Monday.

The blackout originated at an electricity transmission point between the power stations at Argentina’s Yacyretá dam and Salto Grande in the country’s northeast “when the system was getting too much power” Lopetegui said. Although these types of failures have happened in other countries as well, he said a chain of events took place that caused a total disruption.