BBC: A massive electrical failure has left all of Argentina and Uruguay without power, according to a major Argentine electricity provider.
Reports said the power cut had also affected parts of Brazil and Paraguay.
Argentine media said the power cut occurred shortly after 07:00 (12:00 GMT), causing trains to be halted and failures with traffic signalling.
It came as people in parts of Argentina were preparing to go to the polls for local elections.
“A massive failure in the electrical interconnection system left all of Argentina and Uruguay without power,” electricity supplier company Edesur said in a tweet.