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

Power had almost fully returned to Spain early Tuesday morning as many questions remained about what caused one of Europe’s most severe blackouts across Spain and Portugal. By 7:00a.m., Spanish electricity operator Red Eléctrica said that more than 99% of energy demand had been restored.

Spain and Portugal were returning to some semblance of normality early Tuesday, with many questions remaining about what caused one of Europe’s worst blackouts in years across the Iberian peninsula the previous day.