A major blackout hit Buenos Aires Wednesday, cutting off power to more than 1 million homes, government buildings and public transportation.

The outage was reportedly caused by the failure of two high-voltage power lines as a heat wave has driven energy demands to record levels, the BBC reported.

The city’s metro system was disrupted and traffic lights went out. The Argentine Congress building and presidential palace were also affected.

Power was restored later in the evening.

Buenos Aires has experienced three days of temperatures above 90 degrees Fahrenheit, which has put a large strain on the city’s energy grid as households use air-conditioning to cope with the heat, though the actual cause of the blackout has yet to be determined.