A massive power outage is impacting Spain and Portugal, knocking out key services and forcing the evacuation of subway systems in both countries, reports say.

Most of Spain and all of Portugal were hit by a major blackout that impacted public transport, airports and phone service, leaving authorities scrambling to find the causes for one of the worst outages in Europe in years.

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.