Spain, Portugal, and parts of southern France experienced a massive power outage on Monday, affecting millions of people, according to electricity grid operators. The cause of the outage has not yet been determined.

Spain’s state-owned company Red Eléctrica announced via the platform X (formerly Twitter) that power had been gradually restored in both the northern and southern regions of the country, according to AFP.

Meanwhile, Portuguese company REN confirmed that the entire Iberian Peninsula, including Spain and Portugal, along with parts of southern France, was impacted by the blackout.

Emergency teams in the affected countries are working to fully restore electricity, while authorities have yet to provide an official explanation for what is being described as one of the largest power disruptions to hit the region in recent years.