Before dawn, power was gradually returning to several regions across Spain and Portugal as the nations reeled from the still-unexplained widespread blackout that had turned airports and train stations into campgrounds for stranded travelers.

Power has been restored to tens of millions of people across almost all of Spain and Portugal, but disruptions to transport services were expected to stretch into a second day as questions mount over what caused a massive blackout.

A widespread power outage hit Spain and Portugal, affecting millions of people who live across Europe's Iberian Peninsula.