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.
The combined population of Argentina and Uruguay is about 48 million people.
Among the affected provinces in Argentina were Santa Fe, San Luis, Formosa, La Rioja, Chubut, Cordoba and Mendoza, reports said.
Social media reports of the power were widespread - from the capital Buenos Aires in the north, to Mendoza in the west and Comodoro Rivadavia in the south, among many other cities.
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