BUENOS AIRES, Argentina—A massive blackout left tens of millions of people without electricity in Argentina and Uruguay on Sunday, June 16, after an unexplained failure in the neighboring countries’ interconnected power grid. Authorities were working frantically to restore power, but by mid-afternoon about half of Argentina’s 40 million people were still in the dark.

A turned off sign in a gas station supposed to show prices during the blackout, in Buenos Aires, Argentina, on June 16, 2019. Tomas F. Cuesta/AP Photo