The hunt has begun for the cause of a massive blackout across Spain, Portugal and parts of France that halted trains, bank machines and traffic lights, in one of Europe's biggest ever power system collapses.

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.

Much of Spain’s power grid was operating normally on Tuesday, a day after a blackout affected critical infrastructure across the Iberian Peninsula.