A widespread and unexplained power outage knocked out electricity in most of Spain and Portugal on Monday, shutting off traffic lights and causing chaos at airports, train stations and on the roads.

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.

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.