An unprecedented blackout brought much of Spain and Portugal to a standstill Monday, stopping trains, cutting phone service and shutting down traffic lights and ATMs for millions of people across the Iberian Peninsula. Spanish power distributor Red Eléctrica declined to speculate on the cause of the power outage that began around 12:30 p.m. Madrid time and said restoring power fully could take six to 10 hours. Head of operations Eduardo Prieto told journalists it was unprecedented, calling the event “exceptional and extraordinary.” By 8:35 p.m., only 35% of energy demand had been restored, Prieto said hours later. Spain’s Prime Minister Pedro Sánchez said a “strong oscillation” in the European grid was behind the outage but the cause was still being determined. He asked the public to refrain from speculation, and urged people to call emergency services only if really necessary. It was the second serious European power outage in less than six weeks after a March 20 fire shut down Heathrow Airport in the U.K., and it came as authorities across Europe gird against sabotage backed by Russia. The Portuguese National Cybersecurity Center in a statement said there was no sign the outage was due to a cyberattack. Teresa Ribera, European Commission executive vice president in charge of promoting clean energy, indicated the same to journalists in Brussels and called the power outage “one of the most serious episodes recorded in Europe in recent times.” Spanish and Portuguese capitals affected The outage began after midday. Offices closed and traffic was snarled in major cities. In Barcelona civilians directed traffic. Train services in both countries stopped, leaving tens of thousands of passengers stranded. It wouldn’t be possible to restart trains later Monday even if the power returned, Spain’s Transportation Minister Oscar Puente posted on social media. The subway systems shut down. “I don’t know how I am going to get home,” said Barcelona resident Ivette Corona as she watched a large group of people fail to get on a bus that briefly stopped to squeeze in a couple of passengers. In Madrid, hundreds of people at a bus stop that takes travelers to the airport were trying to hitch-hike. Some held improvised signs to convince drivers to take them. “I’ve been here for almost three hours, trying to get someone to take me to the airport because my family arrived today and I can’t talk to them. This is terrifying,” said Jessica Fernandez, one of the many people at the bus stop.