Widespread power outages upended life for millions across Spain and Portugal — and, briefly, parts of France — on Monday.
Traffic lights went dark at busy intersections. Trains stopped in the middle of a workday. And long lines formed at A.T.M.s and grocery stores, where credit card readers stopped working.
By Tuesday morning, the outages were mostly over, but their cause was still under investigation.
Here’s what we know.
Power has mostly been restored to the region.
Spain’s national power company said early Tuesday that nearly all power demand in Peninsular Spain had been met by 6 a.m.
Portugal’s electricity and gas supplier, REN, said that power had been restored to all of its substations by late Monday.
The electrical grid operator in France, where the outage briefly affected households in the Basque region, said all power had been restored.
The cause remains under investigation.
Spain’s prime minister, Pedro Sánchez, said that officials were still investigating the causes of the outage.
Spain’s national power company, Red Eléctrica, said on Tuesday morning that it had ruled out a cyberattack or meteorological causes, and that human error was unlikely.
Portugal’s national energy supplier, E-Redes, cited an unspecified “problem in the European electricity grid.”
António Leitão Amaro, a senior official in the Portuguese government, also said there was no evidence of a cyberattack. REN denied reports that an unspecified “atmospheric phenomenon” was to blame.
Hospitals, banks and travel were disrupted.
During the outages, there were widespread problems connecting to the internet and to phone networks across Spain and Portugal. Mr. Sánchez urged people to make only brief calls on their cellphones.
Hospitals in Spain were forced to run on generators. Portuguese banks and schools closed. Spain’s national rail company said that trains had stopped operating at all stations. Subways in several cities, including Valencia and Madrid, were halted. The Madrid Open tennis tournament was suspended. And people crammed into stores to buy food and other essentials as clerks used pen and paper to record cash-only transactions.
Diana Alfia, an employee at a hostel in Lisbon, said that some people had gone to the beach since there was not much else to do, and some tourists walked miles from the airport into the city because Uber and public transportation were not available.
Power went out amid high temperatures.
According to Spain’s meteorological agency, AEMET, temperatures across the country were between 60 and 70 degrees Fahrenheit around the time of the power outages. By the end of the day, highs had climbed to between 82 and 87 degrees.
That was higher than usual: In April, temperatures in Spain average around 64 degrees in central and northern regions and about 70 degrees in the south.
When asked whether the outages were connected to the heat, Bruno Silva, a spokesman for REN, was skeptical. “No, I hope not,” he said.
Other European outages have halted daily life.
More than 50 million people in Italy were left in the dark for almost a full day in 2003 after a line between Switzerland and Italy was overloaded. It was considered the worst day of blackouts in the country since World War II.
In 2006, 10 million people in Germany were briefly without power after the northwestern part of the country’s power grid became overloaded.
And last year, much of the Balkans was without power for several hours during a heat wave in which temperatures soared to 40 degrees Celsius, or over 100 degrees Fahrenheit.
The power grids in Europe are interconnected, and an overload or issue in one area can spread to another country.
Nazaneen Ghaffar, Mike Ives and John Yoon contributed reporting.
