Power is being restored to Argentina and Uruguay after a massive electrical failure left large parts of both countries without electricity. Argentine President Mauricio Macri has promised a full investigation.
Argentine media said the power cut occurred shortly after 07:00 (11:00 BST), causing trains to be halted and failures with traffic signalling.
The blackout was prompted by a failure in an electrical grid that serves both Argentina and Uruguay.
The outage occurred as people in Argentina were preparing to go to the polls for local elections, delaying voting in several regional provinces.
Parts of Paraguay were also affected, a state energy company said.
“A massive failure in the electrical interconnection system left all of Argentina and Uruguay without power,” electricity supply company Edesur said in a tweet.
Alejandra Martinez, a spokeswoman for the company, described the power cut as unprecedented.
“This is the first time something like this has happened across the entire country.”
Citing official sources, Argentine media reported that the outage was linked to a failure in the transmission of electricity from the Yacycretá hydroelectric dam.