Spain and Portugal are reeling from a massive, unexplained power outage that knocked out traffic lights, caused chaos on roads and in airports, and prompted both countries to declare a state of emergency.

Power outages left tens of millions of people in Spain and Portugal in the dark on Monday. The blackouts shut off phone service and traffic lights, stopped trains, and cut off water access for U.S. Open champion Coco Gauff following her win at the Madrid Open, along with countless others.