Authorities are still largely in the dark about what caused a massive blackout across Argentina, Uruguay and Paraguay that affected tens of millions of people.
Argentine President Mauricio Macri has promised a thorough investigation into what he called an "unprecedented" outage, one that raised questions about flaws in South America's 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.
Argentine Energy Secretary Gustavo Lopetegui said the blackout began with a failure in the country's "interconnection system," adding that it happens in other countries as well.
But he said a chain of events took place later, causing a total disruption.
"This is an extraordinary event that should have never happened," he told a news conference. "It's very serious. We can't leave the whole country all of a sudden without electricity."
The collapse began at about 7 am Sunday, with Argentina's population of 44 million and residents of neighbouring Uruguay and some areas of Paraguay waking up in the dark.
Public transportation halted in Buenos Aires, while phone and internet communications were disrupted, water supplies were cut off and shops were forced to close. Patients dependent on home medical equipment were urged to go to hospitals with generators.
Power was fully restored by Sunday night. But the outage ignited questions about Argentina's preparedness and lack of investment in the power system.
Energy officials defended the strength of the Argentine system, saying it's "robust". But the grid has been known for being in a state of disrepair, with substations and cables that were insufficiently upgraded as power rates remained largely frozen for years.
Argentines are also frustrated with high utility costs and the blackout could trigger more protests against Macri's government just as he seeks re-election in October.
The power failure on Sunday comes three months after crisis-torn Venezuela suffered its worst power outage with the lack of electricity endangering hospital patients.
Australian Associated Press