The country’s top officials were trying to determine the cause of an outage that left tens of millions of people across the Iberian Peninsula without power.

Spanish prime minister Pedro Sánchez said a nationwide blackout of this scale had never happened before in Spain. He added that the underlying cause remains unclear.

As factories, stores and hotels across Spain and Portugal gradually returned to normal on Tuesday after a huge blackout the day before, business associations and companies began counting the cost.