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.

See photos of the massive power outage that affected millions of people in Spain and Portugal due to an "induced atmospheric vibration."

Power cuts have impacted as many as 50 million people across Spain and Portugal - causing huge disruption to public transport, airports and vital telecommunications networks