Electricity returned Tuesday in Spain and Portugal after long hours of an "exceptional" power outage of unknown origin, causing chaos across the Iberian Peninsula.

In various neighborhoods of Madrid, the return of electricity was often met with applause and cheers from residents in the evening, after a long day without power and often without internet or mobile phone service.

By 5 a.m. Spanish time (3 a.m. GMT), 92.09% of the national power supply was restored in mainland Spain, announced the grid operator REE.

In Portugal, according to the grid operator, about 6.2 million households had power again in the middle of the night out of a total of 6.5 million.

Spanish Prime Minister Pedro Sanchez refrained from offering an explanation for the blackout that began at 10:33 a.m. GMT Monday (12:33 p.m. in Spain).

"No hypothesis" is "ruled out," he emphasized during a press conference. "Never" had there been such a "collapse" of the Spanish grid, he continued, noting that "15 gigawatts" of electricity had been lost from the Spanish grid, all "in barely five seconds." "Fifteen gigawatts correspond approximately to 60% of Spain's electricity demand at that time of day," described the head of the government.

His Portuguese counterpart Luis Montenegro, meanwhile, mentioned a "serious and unprecedented situation" whose origin is most likely in Spain.

The gradual return to normal was good news on both sides of the border, after a long day juggling difficulties, between closed subways, packed buses, stranded trains, and extremely difficult communications.

Massive traffic jams

In Lisbon, "I was at the office when all of a sudden my computer turned off," testified to AFP Edgar Parreira, a 34-year-old advertiser.

"Initially we thought it was a problem in the building, then we started calling our relatives and realized it was the whole city and then it was happening in Spain too," he added.

In central Madrid, residents and tourists gathered in front of the facades of chic hotels or banks, to enjoy a few moments of free Wi-Fi still powered by generators.

In the evening, thousands of people had to patiently cross the city, attempting to get home on foot. The main arteries of the capital were engulfed in massive traffic jams, amidst which pedestrians zigzagged trying to make their way.

Similar scenes occurred in Barcelona, where many residents took to the streets, phone in hand, in search of a hypothetical network.

Long improvised lines stretched for several hundred meters at bus stops. "Look, the queue takes a thousand turns," despaired Rosario Pena, a 39-year-old fast-food employee in Madrid.

A few hours later, traffic lights and shop fronts lit up again, a sign of an improvement in the situation, at least in the Spanish capital.

In the Madrid region alone, 286 operations took place to rescue people trapped inside elevators, according to regional authorities.

Trains stopped

Tuesday morning, three trains were still halted in Spain with passengers on board, according to Transport Minister Oscar Puente.

High-speed train traffic is expected to resume normally on Tuesday morning on several main lines, including Madrid-Barcelona and Madrid-Valencia, but remains disrupted on others like Barcelona-Alicante and between Madrid and Galicia (northwest), wrote Puente on X.

Air traffic was also highly disrupted, particularly at the airports of Madrid, Barcelona, and Lisbon, according to the European air traffic monitoring body Eurocontrol. But the Spanish Prime Minister highlighted in the evening that only 344 flights out of 6,000 scheduled in the country Monday had been canceled.

"There are no security issues. Our hospital system is functioning properly," assured Sanchez Monday. Indeed, despite the chaos and confusion, the atmosphere remained calm and friendly in the streets of Madrid throughout the outage.

Supply was partially restored thanks to interconnections with France and Morocco, and gas and hydroelectric power plants were "reactivated across the country," according to Sanchez.

Spanish nuclear plants were shut down, a normal safety procedure in the event of a power outage.

In Europe, a failure of the German network on November 4, 2006, plunged 10 million people into darkness, half in France and the rest in Germany, Belgium, the Netherlands, Italy, and Spain, for nearly an hour.

Three years earlier, the entire country of Italy, except Sardinia, was deprived of electricity on September 28, 2003.