BARCELONA, Spain (AP) — A major power outage in Spain and Portugal has knocked out subway networks, traffic signals and ATMs. Spanish power distributor Red Eléctrica said restoring power to large parts of the country could take 6-10 hours. The company declined to speculate on the causes of the blackout Monday.

A massive power cut hit large parts of Spain and Portugal on Monday, causing widespread chaos and disruption. The outage left millions of people without electricity, while internet and phone networks were also down. Trains were cancelled and evacuated in some regions, traffic lights stopped working amid mounting delays at airports.

A countrywide power outage impacted Spain—as well as swaths of Portugal and smaller portions of France—Monday afternoon, affecting essential services and wreaking chaos across the Iberian Peninsula. The cause of the outage is currently being investigated by Spanish and Portuguese officials and ministers.