Spain and Portugal experienced a widespread power outage on Monday, leaving millions without electricity in a snap blackout. In Portugal, official sources told domestic media that the outage, which hit around late morning local time,

Play was halted at the Madrid Open tennis tournament, while the Spanish capital's metro system ground to a stop.

Red Eléctrica, Spain’s electricity grid operator, ruled out a cyberattack, human error or unusual weather. Experts say it could take weeks to determine the cause.