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 massive power cut hit large parts of Spain and Portugal on Monday, causing widespread chaos and disruption. The outage left millions of people without electricity, while internet and phone networks were also down. Trains were cancelled and evacuated in some regions, traffic lights stopped working amid mounting delays at airports.

Play is expected to continue at the Madrid Open today after most of Monday’s matches were cancelled as widespread power outages hit the Iberian Peninsula.