A failure in "high-voltage lines" left more than 300,000 people in Buenos Aires without electricity for four hours on Tuesday.
The cut, which affected neighbourhoods in the centre and south of the city, came on a day of oppressive heat and high commercial activity ahead of the Christmas holidays.
The blackout "occurred due to an intentional fire that affected high-voltage lines," concessionary firm Edesur said in a post on social networks.
At the time of the failure, at dusk, there were "a total of 305,172 users" without electricity, according to the national regulator. Four hours later there were only "2,221 users without electricity," the National Electricity Regulation Entity said in a statement.
The fire started in an uninhabited area with wild vegetation, next to an electrical substation, firefighters told the C5N television news channel.
"A failure in the high-voltage network produced a cut in the supply to residents of the south-central zone of Buenos Aires," Edesur said in a statement.
The blackout affected homes, shops and traffic lights, prompting confusion and snarling traffic jams in some neighbourhoods.
Some 14 million people live in the Buenos Aires metropolitan area, which is supplied by firms Edesur and Edenor.
While the power cut was ongoing, local weather officials said temperatures stood at 32 degrees Celsius.