Spain and Portugal are racing the setting sun as they respond to a massive, unexplained power outage that knocked out traffic lights, caused chaos on roads and in airports, and threatened to plunge tens of millions of people into darkness on Monday.

Spanish power distributor Red Eléctrica said that restoring power fully to the country and neighboring Portugal could take 6-10 hours.

Several airports, including Madrid airport, which is Spain's busiest, had no electricity, El Mundo reported. Major cities including Barcelona, Seville and Valencia were without power. Parts of France were also affected by power loss.